Liquid crystal display device comprising first and second electrodes wherein the second electrode is connected with a source electrode without passing through a first insulating film

ABSTRACT

To form a sufficiently large storage capacitor, a liquid crystal display device includes a liquid crystal display panel having a first substrate, a second substrate, and a liquid crystal held between the first substrate and the second substrate, the liquid crystal display panel having multiple pixels arranged in matrix. The first substrate has, in a transmissive display area provided in each of the pixels, a laminated structure containing a first transparent electrode, a first insulating film, a second transparent electrode, a second insulating film, and a third transparent electrode which are laminated in this order. The first transparent electrode and the second transparent electrode are electrically insulated from each other and together form a first storage capacitor through the first insulating film, and the second transparent electrode and the third transparent electrode are electrically insulated from each other and together form a second storage capacitor through the second insulating film.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a Continuation of U.S. application Ser. No.13/718,467 filed on Dec. 18, 2012, which is a Continuation of U.S.application Ser. No. 13/550,330 filed on Jul. 16, 2012, which is aContinuation of U.S. application Ser. No. 12/230,417 filed on Aug. 28,2008. Priority is claimed based on U.S. application Ser. No. 13/718,467filed on Dec. 18, 2012, which claims priority from U.S. application Ser.No. 13/550,330 filed on Jul. 16, 2012, which claims priority from U.S.application Ser. No. 12/230,417 filed on Aug. 28, 2008, which claimspriority from Japanese application JP 2007-228412 filed on Sep. 4, 2007,the content of which is hereby incorporated by reference into thisapplication.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a liquid crystal display device, andmore particularly, to a technology effectively applied to a liquidcrystal display device that has a liquid crystal display panel with finepixel dimensions.

2. Description of the Related Art

A liquid crystal display device is composed of a pair of substrates (forexample, glass substrates) and a liquid crystal composition sealed in agap between the substrates. Specifically, in the case of an in-planeswitching (IPS) liquid crystal display device, for example, thin filmtransistors with amorphous silicon or other semiconductor layers, pixelelectrodes, signal lines, scanning lines, gate electrodes, counterelectrodes, and the like are formed on one of the substrates(hereinafter, referred to as TFT substrate), whereas a light shieldingfilm, a color filter, and the like are formed on the other substrate(hereinafter, referred to as CF substrate). The TFT substrate and the CFsubstrate are arranged to face each other across a predeterminedinterval, which is kept by a spacer, and are sealed with a sealant. Aliquid crystal composition is sealed between the substrates.

Pixels in a common liquid crystal display device each have a storagecapacitor. The storage-capacitor is used mainly to prevent feed-throughvoltage caused by a voltage change in the scanning line or the signalline from affecting the voltage of the pixel electrode during a holdperiod in which the thin film transistor is off.

The storage capacitor is implemented by, for example, the following fourstructures:

(1) Upper layer transparent pixel electrode/insulating film/lower layertransparent storage capacitor electrode.

(2) Upper layer transparent pixel electrode/insulating film/lower layermetal storage capacitor electrode.

(3) Upper layer metal source (or drain) electrode/insulating film/lowerlayer metal storage capacitor electrode.

(4) Upper layer metal source (or drain) electrode/insulatingfilm/intermediate metal storage capacitor electrode/insulatingfilm/lower layer polycrystalline silicon source (or drain) electrode.

The above-mentioned structure (1) is described in, for example, JP08-179363 A, and the above-mentioned structure (4) is described in, forexample, JP 2000-180900 A.

SUMMARY OF THE INVENTION

When one of the electrodes that constitute the storage capacitor ismetal as in the above-mentioned structures (2) to (4), thenon-transparent metal part makes it difficult to raise the apertureratio, particularly in the case of a transmissive liquid crystal displaydevice. It is therefore preferred to employ transparent conductivematerials for both of the electrodes of the storage capacitor as in theabove-mentioned structure (1).

However, reducing the pixel dimensions for the purpose of obtaining anultra-high definition liquid crystal display panel, such as one forportable terminal that have a VGA-level resolution, accordingly reducesthe area per pixel that can be used to form the electrodes of thestorage capacitor.

The insulating film that forms the storage capacitor can be thinned inresponse to the reduction in electrode area only to a limited degree,because the insulating film needs to retain a certain thickness inconsideration of manufacture yield. Then allocating the entiretransmissive display area in a single pixel to the electrodes of thestorage capacitor that has the structure (1) is not enough to preventthe storage capacitor from being smaller.

The reduction in capacitance of the storage capacitor is more prominentin IPS liquid crystal display panels, where one of the electrodes is aplanar transparent electrode and the other electrode is a comb-shapedtransparent electrode which is formed above the former electrode with aninsulating film sandwiched between the two. This structure (comb-shapedtransparent electrode/insulating film/flat board-like transparentelectrode) also functions as the storage capacitor but, since areduction in dimensions per pixel reduces the comb teeth of the upperlayer transparent electrode in length and number, the capacitance of thestorage capacitor is made even smaller.

A parasitic capacitor, which is formed between the pixel electrode andthe scanning line or the signal line, is also made smaller by areduction in per-pixel dimensions due to the coupling length beingshortened by the reduction. However, compared to the way the capacitanceof the storage capacitor, which is almost dependent on the per-pixelarea, is reduced the reduction in capacitance of the parasitic capacitoris more gradual. Rather, the parasitic capacitor is hardly reduced incapacitance since obtaining a sufficient aperture ratio requires closingthe planar gap between the pixel electrode and the scanning line or thesignal line (or increasing the overlapping area), which reduces thecoupling interval of the parasitic capacitor. This makes it difficult toform a sufficiently large storage capacitor balanced with the parasiticcapacitor even in the conventional structure (1).

If the storage capacitor is not large enough in relation to theparasitic capacitor, the voltage of the pixel electrode is easilyaffected by feed-through voltage, which is caused by a voltage change inthe scanning line or the signal line, during a hold period in which thethin film transistor is off. The resultant problem resides in that theimage quality is degraded from such phenomena as smearing and crosstalk.

The present invention has been made to solve the aforementioned problemsof prior art, and an object of the present invention is therefore toprovide a technology with which a sufficiently large storage capacitorcan be formed in a display device that has a liquid crystal displaypanel with fine pixel dimensions.

The above-mentioned and other objects and novel characteristics of thepresent invention will be clarified by the descriptions herein and theaccompanying drawings.

Representative aspects of the present invention are summarized asfollows.

(1) A liquid crystal display device including: a liquid crystal displaypanel having a first substrate, a second substrate, and a liquid crystalheld between the first substrate and the second substrate, the liquidcrystal display panel having multiple pixels arranged in matrix; and atransmissive display area provided in at least part of each of thepixels, having a laminated structure containing a first transparentelectrode, a first insulating film, a second transparent electrode, asecond insulating film, and a third transparent electrode which arelaminated in this order with the first transparent electrode closest tothe first substrate. The first transparent electrode and the secondtransparent electrode are electrically insulated from each other andtogether form a first storage capacitor through the first insulatingfilm, and the second transparent electrode and the third transparentelectrode are electrically insulated from each other and together form asecond storage capacitor through the second insulating film.

(2) In the aspect (1), at least one of the first insulating film and thesecond insulating film is a laminate of multiple insulating films.

(3) In the aspect (1), the first insulating film and the secondinsulating film are formed from one of the same material and differentmaterials.

(4) In the aspect (1), the first insulating film and the secondinsulating film have one of the same refractive index and differentrefractive indices.

(5) In the aspect (1), the transmissive display area provided in atleast part of each of the multiple pixels has a third insulating film,which is placed on the first substrate side of the first transparentelectrode.

(6) In the aspect (5), the third insulating film has a dielectricconstant equal to or lower than a dielectric constant of one of thefirst insulating film and the second insulating film.

(7) In the aspect (5), the third insulating film is a laminate ofmultiple insulating films.

(8) In the aspect (5), the first insulating film, the second insulatingfilm, and the third insulating film are formed from one of the samematerial and different materials.

(9) In the aspect (1), the first transparent electrode, the secondtransparent electrode, and the third transparent electrode are formedfrom one of the same material and different materials.

(10) In the aspect (1), the first transparent electrode, the secondtransparent electrode, and the third transparent electrode have one ofthe same refractive index and different refractive indices.

(11) In the aspect (1), the first transparent electrode, the secondtransparent electrode, and the third transparent electrode have one ofthe same thickness and different thicknesses.

(12) In the aspect (1), the first transparent electrode, the secondtransparent electrode, the third transparent electrode, the firstinsulating film, and the second insulating film are respectively set tosuch refractive indices and thicknesses that, when combined, provide ano-reflection condition with respect to at least, a part of light whosewavelength is within the visible light range.

(13) In the aspect (5), the first transparent electrode, the secondtransparent electrode, the third transparent electrode, the firstinsulating film, the second insulating film, and the third insulatingfilm are set respectively to such refractive indices and thicknessesthat, when combined, provide a no-reflection condition with respect toat least a part of light whose wavelength is within the visible lightrange.

(14) In the aspect (1), the first transparent electrode, the secondtransparent electrode, and the third transparent electrode have one ofthe same area and different areas.

(15) In the aspect (1), an overlap between the first transparentelectrode and the second transparent electrode which is measured by areais the same as, or differs from, an overlap between the secondtransparent electrode and the third transparent electrode which ismeasured by area.

(16) In the aspect (1), the first substrate has a reflective electrodein a reflective display area, which is provided in at least part of eachof the multiple pixels, and the reflective electrode is electricallyconnected to at least one of the first transparent electrode, the secondtransparent electrode, and the third transparent electrode.

(17) In the aspect (1), the third transparent electrode has multiplecomb-teeth electrodes, and the liquid crystal display device generatesan electric field that has a component parallel to a surface of thefirst substrate between the third transparent electrode and the secondtransparent electrode, and uses the electric field to drive a liquidcrystal on the surface side of the third transparent electrode.

(18) In the aspect (1), the third transparent electrode has a shape of aflat board with a slit, and the liquid crystal display device generatesan electric field that has a component parallel to a surface of thefirst substrate between the third transparent electrode and the secondtransparent electrode, and uses the electric field to drive a liquidcrystal on the surface side of the third transparent electrode.

(19) In the aspect (1), each of the multiple pixels has a fourthtransparent electrode, which is placed on the second substrate side, andthe liquid crystal display device generates an electric field betweenthe fourth transparent electrode and the third transparent electrode,and uses the electric field to drive a liquid crystal on the surfaceside of the third transparent electrode.

(20) In any one of the aspects (1) to (18), each of the multiple pixelshas a thin film transistor, the third transparent electrode is a counterelectrode, the second transparent electrode is a pixel electrode, andthe first transparent electrode is a storage capacitor electrode.

(21) In the aspect (20), the first insulating film is a laminate of agate insulating layer and an interlayer insulating layer with the gateinsulating layer placed closer to the first substrate, the thirdtransparent electrode is connected to a common electrode wiring line,the second transparent electrode is connected to a first electrode ofthe thin film transistor through an opening formed in the interlayerinsulating layer, and the first transparent electrode is connected to astorage capacitor wiring line.

(22) In the aspect (20), the first insulating film is a laminate of agate insulating layer and an interlayer insulating layer with the gateinsulating layer placed closer to the first substrate, the firsttransparent electrode is connected to a common electrode wiring line,the second transparent electrode is connected to a first electrode ofthe thin film transistor through an opening formed in the interlayerinsulating layer, and the third transparent electrode is connected toone of the first transparent electrode and the common electrode wiringline through openings formed in the gate insulating layer, theinterlayer insulating layer, and the second insulating film.

(23) In the aspect (20), the first transparent electrode is connected toa storage capacitor wiring line, the second transparent electrode isconnected to a first electrode of the thin film transistor, and thethird transparent electrode is connected to a common electrode wiringline.

(24) In the aspect (20), the first transparent electrode is connected toa common electrode wiring line, the second transparent electrode isconnected to a first electrode of the thin film transistor, and thethird transparent electrode is connected to one of the first transparentelectrode and the common electrode wiring line through openings formedin the first insulating film and the second insulating film.

(25) In the aspect (20), the liquid crystal display device has aninterlayer insulating layer formed above a first electrode of the thinfilm transistor, the first transparent electrode is formed above theinterlayer insulating layer, the first transparent electrode isconnected to a common electrode wiring line, the second transparentelectrode is connected to the first electrode of the thin filmtransistor through openings formed in the interlayer insulating layerand the first insulating film, and the third transparent electrode isconnected to one of the first transparent electrode and the commonelectrode wiring line through openings formed in the first insulatingfilm and the second insulating film.

(26) In the aspect (20), the liquid crystal display device has aninterlayer insulating layer formed above a first electrode of the thinfilm transistor, the first transparent electrode is formed above theinterlayer insulating layer, the third transparent electrode isconnected to a common electrode wiring line, the second transparentelectrode is connected to the first electrode of the thin filmtransistor through openings formed in the interlayer insulating layerand the first insulating film, the first transparent electrode isconnected to an insular transparent electrode pattern which is formedwithin an opening in the first insulating film, and the insulartransparent electrode pattern is connected to the common electrodewiring line through an opening formed in the second insulating film.

(27) In the aspect (21) or (23), the common electrode wiring line andthe storage capacitor wiring line have one of the same voltage anddifferent voltages.

(28) In the aspect (20), the first transparent electrode in one pixel isseparated from the first transparent electrode in another pixel.

(29), In the aspect (20), the first transparent electrode is one ofcommon on a pixel row basis to be shared by pixels in one pixel row,common on a pixel column basis to be shared by pixels in one pixelcolumn, and shared by all pixels.

(30) In the aspect (20), the third transparent electrode in one pixel isseparated from the third transparent electrode in another pixel.

(31), In the aspect (20), the third transparent electrode is one ofcommon on a pixel row basis to be shared by pixels in one pixel row,common on a pixel column basis to be shared by pixels in one pixelcolumn, and shared by all pixels.

(32) In the aspect (20), one of the first transparent electrode and thesecond transparent electrode is connected to a common electrode wiringline, the common electrode wiring line is provided for each pixel row,and the common electrode wiring line in each pixel row is shared.

(33) In the aspect (20), one of the first transparent electrode and thesecond transparent electrode is connected to a common electrode wiringline, the common electrode wiring line is provided for each pixel row,and the common electrode wiring line in one pixel row is independentfrom the common electrode wiring line in another pixel row.

(34) In the aspect (21) or (23), the storage capacitor wiring line isprovided for each pixel row, and the storage capacitor wiring line ineach pixel row is shared.

(35) In the aspect (21) or (23), the storage capacitor wiring line isprovided for each pixel row, and the storage capacitor wiring line inone pixel row is independent from the storage capacitor wiring line inanother pixel row.

(36) In the aspect (20), the first transparent electrode and at leastpart of the first electrode of the thin film transistor form a thirdstorage capacitor through an insulating film that is inserted betweenthe first transparent electrode and the at least part of the firstelectrode of the thin film transistor.

(37) In the aspect (21) or (23), part of the capacitor storage wiringline and at least part of the first electrode of the thin filmtransistor form a third storage capacitor through an insulating filmthat is inserted between the part of the storage capacitor wiring lineand the at least part of the first electrode of the thin filmtransistor.

(38) In any one of the aspects (1) to (19), each of the multiple pixelshas a thin film transistor, the first transparent electrode and thethird transparent electrode are pixel electrodes, and the secondtransparent electrode is a counter electrode.

(39) In the aspect (38), the first transparent electrode is connected toa first electrode of the thin film transistor, the second transparentelectrode is connected to a common electrode wiring line, and the thirdtransparent electrode is connected to the first electrode of the thinfilm transistor through openings formed in the first insulating film andthe second insulating film.

(40) In the aspect (38), the first insulating film is a laminate of agate insulating layer and an interlayer insulating layer with the gateinsulating layer placed closer to the first substrate, the firsttransparent electrode is connected to a first electrode of the thin filmtransistor through an opening formed in the gate insulating layer, thesecond transparent electrode is connected to a common electrode wiringline, and the third transparent electrode is connected to the firstelectrode of the thin film transistor through openings formed in theinterlayer insulating layer and the second insulating film.

(41) In the aspect (38), the liquid crystal display device has aninterlayer insulating layer formed above a first electrode of the thinfilm transistor, the first transparent electrode is formed above theinterlayer insulating layer, the first transparent electrode isconnected to the first electrode of the thin film transistor through anopening formed in the interlayer insulating layer, the secondtransparent electrode is connected to a common electrode wiring line,and the third transparent electrode is connected to the firsttransparent electrode through openings formed in the first insulatingfilm and the second insulating film.

(42) In the aspect (38), the first insulating film is a laminate of agate insulating layer and an interlayer insulating layer with the gateinsulating layer placed closer to the first substrate, the firsttransparent electrode is connected to the third transparent electrodethrough openings formed in the gate insulating layer, the interlayerinsulating layer, and the second insulating film, the second transparentelectrode is connected to a common electrode wiring line, and the thirdtransparent electrode is connected to a first electrode of the thin filmtransistor through openings formed in the interlayer insulating layerand the second insulating film.

(43) In the aspect (38), the second transparent electrode in one pixelis separated from the second transparent electrode in another pixel.

(44) In the aspect (38), the second transparent electrode is one ofcommon on a pixel row basis to be shared by pixels in one pixel row,common on a pixel column basis to be shared by pixels in one pixelcolumn, and shared by all pixels.

(45) In the aspect (38), the second transparent electrode is connectedto a common electrode wiring line, the common electrode wiring line isprovided for each pixel row, and the common electrode wiring line ineach pixel row is shared.

(46) In the aspect (38), the second transparent electrode is connectedto a common electrode wiring line, the common electrode wiring line isprovided for each pixel row, and the common electrode wiring line in onepixel row is independent from the common electrode wiring line inanother pixel row.

(47) In the aspect (38), the liquid crystal display device has a storagecapacitor wiring line formed on the first substrate side of the firstelectrode of the thin film transistor, and part of the capacitor storagewiring line and at least part of the first electrode of the thin filmtransistor form a third storage capacitor through an insulating filmthat is inserted between the part of the storage capacitor wiring lineand the at least part of the first electrode of the thin filmtransistor.

An effect obtained from the representative embodiments of the presentinvention disclosed in this application is summarized as follows.

According to the present invention, a sufficiently large storagecapacitor can be formed in a liquid crystal display device that has aliquid crystal display panel with fine pixel dimensions.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings:

FIGS. 1A and 1B are sectional views showing a basic sectional structureof a main part of a pixel in a liquid crystal display device accordingto a mode of carrying out the present invention;

FIGS. 2A and 2B are schematic diagrams showing a pixel structure in aliquid crystal display device according to a first embodiment of thepresent invention;

FIG. 3 is a circuit diagram showing an equivalent circuit thatrepresents a single pixel in the liquid crystal display device accordingto the first embodiment and in a liquid crystal display device accordingto a third embodiment of the present invention;

FIGS. 4A to 4H are diagrams showing steps of manufacturing a TFTsubstrate in the liquid crystal display device according to the firstembodiment of the present invention;

FIGS. 5A to 5D are sectional views showing the sectional structures ofterminal portions and interlayer connection portions of the TFTsubstrate in the liquid crystal display device according to the firstembodiment of the present invention;

FIGS. 6A and 6B are schematic diagrams showing a pixel structure in aliquid crystal display device according to a second embodiment of thepresent invention;

FIG. 7 is a circuit diagram showing an equivalent circuit thatrepresents a single pixel in the liquid crystal display device accordingto the second embodiment and in liquid crystal display devices accordingto a fourth, fifth, sixth, seventh, eighth, ninth, and tenth embodimentsof the present invention;

FIGS. 8A to 8G are diagrams showing steps of manufacturing a TFTsubstrate in the liquid crystal display device according to the secondembodiment of the present invention;

FIGS. 9A and 9B are schematic diagrams showing a pixel structure in theliquid crystal display device according to the third embodiment of thepresent invention;

FIGS. 10A to 10G are diagrams showing steps of manufacturing a TFTsubstrate in the liquid crystal display device according to the thirdembodiment of the present invention;

FIGS. 11A to 11D are sectional views showing the sectional structures ofterminal portions and interlayer connection portions of the TFTsubstrate in the liquid crystal display device according to the thirdembodiment of the present invention;

FIGS. 12A and 12B are schematic diagrams showing a pixel structure inthe liquid crystal display device according to the fourth embodiment ofthe present invention;

FIGS. 13A to 13F are diagrams showing steps of manufacturing a TFTsubstrate in the liquid crystal display device according to the fourthembodiment of the present invention;

FIGS. 14A to 14D are sectional views showing the sectional structures ofterminal portions and interlayer connection portions of the TFTsubstrate in the liquid crystal display device according to the fourthembodiment of the present invention;

FIGS. 15A and 15B are schematic diagrams showing a pixel structure inthe liquid crystal display device according to the fifth embodiment ofthe present invention;

FIGS. 16A to 16H are diagrams showing steps of manufacturing a TFTsubstrate in the liquid crystal display device according to the fifthembodiment of the present invention;

FIGS. 17A to 17F are sectional views showing the sectional structures ofterminal portions and interlayer connection portions of the TFTsubstrate in the liquid crystal display device according to the fifthembodiment of the present invention;

FIGS. 18A and 18B are schematic diagrams showing a pixel structure inthe liquid crystal display device according to the sixth embodiment ofthe present invention;

FIGS. 19A to 19H are diagrams showing steps of manufacturing a TFTsubstrate in the liquid crystal display device according to the sixthembodiment of the present invention;

FIGS. 20A to 20D are sectional views showing the sectional structures ofterminal portions and interlayer connection portions of the TFTsubstrate in the liquid crystal display device according to the sixthembodiment of the present invention;

FIGS. 21A and 21B are schematic diagrams showing a pixel structure inthe liquid crystal display device according to the seventh embodiment ofthe present invention;

FIGS. 22A to 22G are diagrams showing steps of manufacturing a TFTsubstrate in the liquid crystal display device according to the seventhembodiment of the present invention;

FIGS. 23A to 23D are sectional views showing the sectional structures ofterminal portions and interlayer connection portions of the TFTsubstrate in the liquid crystal display devices according to the seventhand tenth embodiments of the present invention;

FIGS. 24A and 24B are schematic diagrams showing a pixel structure inthe liquid crystal display device according to the eighth embodiment ofthe present invention;

FIGS. 25A to 25H are diagrams showing steps of manufacturing a TFTsubstrate in the liquid crystal display device according to the eighthembodiment of the present invention;

FIGS. 26A to 26D are sectional views showing the sectional structures ofterminal portions and interlayer connection portions of the TFTsubstrate in the liquid crystal display device according to the eighthembodiment of the present invention;

FIGS. 27A and 27B are schematic diagrams showing a pixel structure inthe liquid crystal display device according to the ninth embodiment ofthe present invention;

FIGS. 28A to 28H are diagrams showing steps of manufacturing a TFTsubstrate in the liquid crystal display device according to the ninthembodiment of the present invention;

FIGS. 29A to 29D are sectional views showing the sectional structures ofterminal portions and interlayer connection portions of the TFTsubstrate in the liquid crystal display device according to the ninthembodiment of the present invention;

FIGS. 30A and 30B are schematic diagrams showing a pixel structure inthe liquid crystal display device according to the tenth embodiment ofthe present invention;

FIGS. 31A to 31G are diagrams showing steps of manufacturing a TFTsubstrate in the liquid crystal display device according to the tenthembodiment of the present invention;

FIGS. 32A to 32J are schematic diagrams showing modification examples ofthe pixel structures in the liquid crystal display devices according tothe first to tenth embodiments of the present invention;

FIGS. 33A to 33H are schematic diagrams showing examples of a pixelstructure in a liquid crystal display device according to a twelfthembodiment of the present invention;

FIG. 34A is a circuit diagram showing an equivalent circuit thatrepresents a single pixel in the liquid crystal display device accordingto the twelfth embodiment of the present invention, and FIG. 34B is acircuit diagram showing a modification example of the equivalent circuitthat represents a single pixel in the liquid crystal display deviceaccording to the twelfth embodiment of the present invention; and

FIGS. 35A to 35C are circuit diagrams showing modification examples ofthe equivalent circuits that represent a single pixel in the liquidcrystal display devices according to the first to tenth embodiments ofthe present invention.

DETAILED DESCRIPTION OF THE INVENTION

Embodiments of the present invention will be described below in detailwith reference to the accompanying drawings.

Throughout the drawings illustrating the embodiments, components thathave an identical function are denoted by the same reference symbol inorder to avoid repetitive descriptions.

[Basic Structure]

FIGS. 1A and 1B show a basic sectional structure of a main part of apixel in a liquid crystal display device according to a mode of carryingout the present invention. Shown in FIG. 1A is a case where the presentinvention is applied to an IPS liquid crystal display device, and shownin FIG. 1B is a case where the present invention is applied to avertical-field driven liquid crystal display device. In either case, atransmissive display area provided in at least a part of each pixel hasa laminated structure in which a first transparent electrode EL1 is puton a first substrate SUB1 and then a first insulating film INS1, asecond transparent electrode EL2, a second insulating film INS2, a thirdtransparent electrode EL3, a first alignment film AL1, a liquid crystallayer LC, a second alignment film AL2, and a second substrate SUB2 arelaminated on top of the first transparent electrode EL1 in the orderstated.

In the case where the liquid crystal display device displays colorimages, the above-mentioned pixels correspond to sub-pixels. In thefollowing description, one sub-pixel in the case of color image displayis treated as one pixel.

The first transparent electrode EL1 and the second transparent electrodeEL2 are electrically insulated from each other, and together form afirst storage capacitor Cst1 through the first insulating film INS1. Thesecond transparent electrode EL2 and the third transparent electrode EL3are electrically insulated from each other, and together form a secondstorage capacitor Cst2 through the second insulating film INS2.

As described in the following embodiments, the first storage capacitorCst1 and the second storage capacitor Cst2 may have the same capacitanceor different capacitances. The transmissive display area may furtherhave a third insulating film INS3, which is placed below the firsttransparent electrode EL1, though not shown in FIGS. 1A and 1B.

The first, second, and third insulating films (INS1 to INS3) may each bea laminate constituted of multiple insulating films. The first, second,and third insulating films (INS1 to INS3) may have the same material,dielectric constant, refractive index, and thickness, or may havedifferent materials, dielectric constants, refractive indices, andthicknesses. The dielectric constant of the third insulating film INS3is desirably equal to or lower than the dielectric constant of the firstinsulating film INS1 or of the second insulating film INS2.

The first, second, and third transparent electrodes (EL1 to EL3) mayhave the same material, refractive index, thickness, and area or mayhave different materials, refractive indices, thicknesses, and areas.Desirably, the refractive indices and thicknesses of the first, second,and third transparent electrodes (EL1 to EL3) and the first, second, andthird insulating films (INS1 to INS3) are set so as to, when combined,provide a no-reflection condition with respect to at least some of lightwhose wavelength is within the visible light range, respectively.

In the IPS liquid crystal display device of FIG. 1A, the thirdtransparent electrode EL3 has a comb teeth shape in plan view, and theliquid crystal layer LC is driven by an electric field E, which isgenerated between the third transparent electrode EL3 and the secondtransparent electrode EL2. The shape of the third transparent electrodeEL3 may instead be like a slip, or a flat board with a slit, or a flatboard with an opening. In the case of a reflective or transflectiveliquid crystal display device that employs an IPS display mode, areflective electrode provided in a reflective display area, which isprovided in at least a part of each pixel, is electrically connected toat least one of the first transparent electrode EL1 and the secondtransparent electrode EL2. The first to third transparent electrodes(EL1 to EL3) can be used in the following two ways:

(1) The second transparent electrode EL2 in one pixel is separated fromthe second transparent electrode EL2 in another pixel to serve as apixel electrode, whereas the first transparent electrode EL1 serves as astorage capacitor electrode and the third transparent electrode EL3serves as a counter electrode. The first transparent electrode EL1 andthe third transparent electrode EL3 may be electrically connected to orelectrically insulated from each other. In the case where the firsttransparent electrode EL1 and the third transparent electrode EL3 areelectrically insulated from each other, the first transparent electrodeEL1 and the third transparent electrode EL3 may have the same voltage ordifferent voltages. In the case of a reflective or transflective liquidcrystal display device that employs an IPS display mode, particularlywhen the reflective electrode is connected to the first transparentelectrode EL1, the reflective electrode may double as a storagecapacitor wiring line.

(2) The first transparent electrode EL1 and the third transparentelectrode EL3 in one pixel are separated from the first and thirdtransparent electrodes EL1 and EL3 in another pixel, and areelectrically connected to each other to serve as pixel electrodes,whereas the second transparent electrode EL2 serves as a counterelectrode. The second transparent electrode EL2 in this case doubles asa storage capacitor electrode. In the case of a reflective ortransflective liquid crystal display device that employs an IPS displaymode, particularly when the reflective electrode is connected to thesecond transparent electrode EL2, the reflective electrode may double asa storage capacitor wiring line.

The vertical-field driven liquid crystal display device of FIG. 1B has afourth transparent electrode EL4, which is shaped like a flat board inplan view, between the second alignment film AL2 and the secondsubstrate SUB2 as a counter electrode. The first transparent electrodeEL1 and the third transparent electrode EL3 in one pixel are separatedfrom the first and third transparent electrodes EL1 and EL3 in anotherpixel, and are electrically connected to each other. The thirdtransparent electrode EL3 serves as a pixel electrode that is shapedlike a flat board in plan view. The liquid crystal layer LC is driven byan electric field generated between the third transparent electrode EL3and the fourth transparent electrode EL4. The shapes of the thirdtransparent electrode EL3 and the fourth transparent electrode EL4 inplan view may be like a flat board with a slit or a flat board with anopening.

In the vertical-field driven liquid crystal display device, the secondtransparent electrode EL2 serves as a storage capacitor electrode, andthe second transparent electrode EL2 and the fourth transparentelectrode EL4 may have the same voltage or different voltages. In thecase of a reflective or transflective liquid crystal display device thatemploys a vertical-field driven liquid crystal display mode, areflective electrode provided in a reflective display area, which isprovided in at least part of each pixel, is electrically connected to atleast one of the first to third transparent electrodes EL1 to EL3. Thereflective electrode may double as a storage capacitor wiring line,particularly when connected to the second transparent electrode EL2. Thevertical-field driven liquid crystal display mode discussed here may bea known technology such as the VA mode, the TN mode, the ECB mode, theOCB mode, and the polymer dispersed type.

Embodiments in which the above-mentioned basic structure is applied toan active matrix liquid crystal display device with thin filmtransistors will now be described.

First Embodiment

A first embodiment of the present invention, as well as second to sixthembodiments of the present invention which will be described later,deals with an IPS liquid crystal display device in which the secondtransparent electrode EL2 serves as a pixel electrode, whereas the firsttransparent electrode EL1 and the third transparent electrode EL3 serveas a storage capacitor electrode and as a counter electrode,respectively.

FIGS. 2A and 2B are schematic diagrams showing a pixel structure in theliquid crystal display device according to the first embodiment of thepresent invention. FIG. 2A shows the sectional structure of a pixel andFIG. 2B shows the plan view structure of the pixel on the TFT substrateside. The sectional structure shown in FIG. 2A corresponds to a viewtaken along the line A-A′ shown in FIG. 2B.

On the first substrate SUB1, scanning lines SCN and as many storagecapacitor wiring lines STG are provided so that the former and thelatter are associated with each other on a one-on-one basis. Signallines SIG intersect with the scanning lines SCN and the storagecapacitor wiring lines STG with a gate insulating film INS11 interposedtherebetween. Each pixel defined by the intersecting scanning lines SCNand signal lines SIG is provided with a thin film transistor TFT, atransparent storage capacitor electrode EL1 (ST), which functions as thefirst transparent electrode, and a transparent pixel electrode EL2 (P),which functions as the second transparent electrode. The transparentstorage capacitor electrode EL1 (ST) and the transparent pixel electrodeEL2 (P) have different areas as shown in FIG. 2B.

The storage capacitor wiring line STG and the transparent storagecapacitor electrode EL1 (ST) partially overlap each other to beelectrically connected to each other. A gate electrode G of the thinfilm transistor TFT is connected to the scanning line SCN, a drainelectrode D of the thin film transistor TFT is connected to the signalline SIG, and a source electrode S of the thin film transistor TFT isconnected to the transparent pixel electrode EL2 (P) through an opening(contact hole) CH1 formed in a passivation film INS12.

A laminate constituted of the passivation film INS12 and the gateinsulating film INS11 is used as the first insulating film INS1. Throughthe first insulating film INS1, the first storage capacitor Cst1 isformed between the transparent storage capacitor electrode EL1 (ST) andthe transparent pixel electrode EL2 (P).

Formed above those electrodes are the second insulating film INS2, whichserves as an interlayer insulating film, a common electrode wiring lineCOM, which is shaped after the shape of the storage capacitor wiringline STG and the signal line SIG, and a transparent counter electrodeEL3 (C), which functions as the third transparent electrode. The secondstorage capacitor Cst2 is formed between the transparent pixel electrodeEL2 (P) and the transparent counter electrode EL3 (C) through the secondinsulating film INS2, whereby the TFT substrate is obtained.

The transparent counter electrode EL3 (C) and the common wiring line COMdirectly overlap each other to be electrically connected to each otherand thereby lower the overall resistance of the counter electrode. Thefirst alignment film AL1 for aligning the liquid crystal layer LC in agiven direction is formed in the topmost layer on the TFT substrate.

On the second substrate SUB2, a light shielding film (black matrix) BM,a color filter FIL whose color varies from one pixel to another, aprotective film (overcoat) OC, and the second alignment film AL2 areformed to obtain a counter substrate.

The first alignment film AL1 and the second alignment film AL2 are eachprocessed in advance so that liquid crystal molecules are aligned in agiven direction. The first substrate SUB1 and the second substrate SUB2are arranged such that their alignment film formation faces are opposedto each other across a predetermined interval, and the gap between thetwo is filled with a nematic liquid crystal composition having apositive dielectric anisotropy to form the liquid crystal layer LC.

The transparent counter electrode EL3 (C) above the transparent pixelelectrode EL2 (P) has multiple slit-like openings SLT which run parallelto one another, and hence an electric field having a component parallelto the surface of the first substrate SUB1 is generated between thetransparent pixel electrode EL2 (P) and the transparent counterelectrode EL3 (C) through the liquid crystal layer LC. The liquidcrystal layer LC is driven by this electric field.

A retardation plate and polarization plate (not shown) are disposedoutside of the first substrate SUB1 and the second substrate SUB2 toobtain a normally black (NB) display mode liquid crystal display device.Drive circuits (not shown) are connected to the scanning lines SCN, thestorage capacitor wiring lines STG, the signal lines SIG, and the commonelectrode wiring lines COM.

FIG. 3 shows an equivalent circuit that represents a single pixel in theliquid crystal display device according to the first embodiment. Thetransparent pixel electrode EL2 (P), or the source electrode S, isprovided with a parasitic capacitor Cgs, which is formed between thegate (G) and source (S) of the thin film transistor TFT, and parasiticcapacitors Cds1 and Cds2, which are formed by the transparent pixelelectrode EL2 (P) and the signal lines SIG, in addition to the firststorage capacitor Cst1, the second storage capacitor Cst2, and a pixelcapacitor Cpx.

When the pixel dimensions are reduced to obtain fine pixels, anequivalent storage capacitor sufficiently large in relation to theparasitic capacitors including Cgs, Cds1, Cds2, and the like can beformed from the parallel capacitance of the first storage capacitor Cst1and the second storage capacitor Cst2. This makes the voltage of thetransparent pixel electrode EL2 (P) less susceptible to feed-throughvoltage, which is caused by a voltage change in the scanning line SCN orthe signal line SIG, during a hold period in which the thin filmtransistor TFT is off. Phenomena called smearing and cross talk can thusbe reduced.

It also reduces the leakage of electric charges accumulated in thetransparent pixel electrode EL2 (P) and the source electrode (S) duringa hold period. Accordingly, the electric field applied to the liquidcrystal layer LC drops less and degradation in image quality can beprevented.

Furthermore, since the first storage capacitor Cst1 and the secondstorage capacitor Cst2 are constituted of the transparent storagecapacitor electrode EL1 (ST), the first insulating film INS1, thetransparent pixel electrode EL2 (P), the second insulating film INS2,and the transparent counter electrode EL3 (C), which are alltransparent, forming a storage capacitor that is sufficiently large inrelation to the parasitic capacitor does not lower the aperture ratio ofthe transmissive display portion. The formation of a sufficiently largestorage capacitor and the securing of a sufficiently high aperture ratioare thus accomplished simultaneously. Those effects of the firstembodiment are shared by the second to sixth embodiments and an eleventhembodiment which will be described later.

In this embodiment and the third embodiment described later, the storagecapacitor wiring line STG in one pixel row and the storage capacitorwiring line STG in another pixel row may receive voltage applicationindependently of each other or commonly. The common electrode wiringline COM and the transparent counter electrode EL3 (C) in one pixel rowmay receive voltage application independently of those in another pixelrow, or the common electrode wiring line COM and the transparent counterelectrode EL3 (C) in one pixel column may receive voltage applicationindependently of those in another pixel column, though, from thestandpoint of reducing the resistance of the counter electrode, it ispreferred to connect the common electrode wiring line COM and thetransparent counter electrode EL3 (C) in one pixel to those in adjacentpixels so that a voltage is applied commonly to all pixels. The voltageof the storage capacitor wiring line STG and the voltage of the commonelectrode wiring line COM may be the same, which does not mean that thetwo always need to match.

FIGS. 4A to 4H show steps of manufacturing the TFT substrate in theliquid crystal display device according to the first embodiment.

In FIG. 4A, a film is formed from a transparent conductive material suchas ITO on the first substrate SUB1, which is a transparent insulatingmember such as a glass substrate. The film is treated by aphotolithography process to form the transparent storage capacitorelectrode EL1 (ST).

In FIG. 4B, a film is formed from a metal material to form the gateelectrode G, the scanning line SCN (not shown), and the storagecapacitor wiring line STG simultaneously by a photolithography process.This layer is called a gate layer. Part of the transparent storagecapacitor electrode EL1 (ST) is overlapped with part of the storagecapacitor wiring line STG, and hence the transparent storage capacitorelectrode EL1 (ST) and the storage capacitor wiring line STG areelectrically connected to each other.

In FIG. 4C, the gate insulating film INS11, which is made of atransparent insulating material such as SiN, SiO, or TaO, and asemiconductor layer a-Si, which is made of amorphous silicon, are formedin succession, and only the semiconductor layer a-Si is treated by aphotolithography process. A heavily doped n-type thin film (not shown)is present on the top face of the semiconductor layer a-Si.

In FIG. 4D, a film is formed from a metal material to form the sourceelectrode S, the drain electrode D, and the signal line SIG (not shown)simultaneously by a photolithography process. This layer is called adrain layer. The heavily doped n-type layer which is not covered withthe drain layer is removed at the same time when the drain layer istreated.

In FIG. 4E, the passivation film INS12 is formed from SiN. Thepassivation film INS12 and the gate insulating film INS11 are treated atonce by a photolithography process. The opening CH1 is formed in aportion of the passivation film INS12 that is located above the sourceelectrode S.

In FIG. 4F, a film is formed from a transparent conductive material suchas ITO and is treated by a photolithography process to form thetransparent pixel electrode EL2 (P). The transparent pixel electrode EL2(P) is electrically connected to the source electrode S through theopening CH1 in the passivation film INS12. A region in which thetransparent storage capacitor electrode EL1 (ST) and the transparentpixel electrode EL2 (P) overlap each other through the laminateconstituted of the gate insulating film INS11 and the passivation filmINS12 serves as the first storage capacitor Cst1.

In FIG. 4G, the second insulating film INS2 is formed from SiN and istreated by a photolithography process. By this photolithography process,a pixel portion is not patterned, whereas openings are opened interminal portions and interlayer connection portions.

In FIG. 4H, a film is formed from a metal material and is treated by aphotolithography process to form the common electrode wiring line COM.

Lastly, a film is formed from a transparent conductive material such asITO to cover the common electrode wiring line COM, and is treated by aphotolithography process to form the transparent counter electrode EL3(C) as the one shown in FIG. 2A. The TFT substrate is thus manufacturedby conducting a photolithography process nine times in total.

The steps of FIGS. 4A to 4F can be adopted from, for example, amanufacturing process of an IPS liquid crystal display device in which acomb-like pixel electrode, or a pixel electrode having a slit, is formedon a planar counter electrode (C) with an interlayer insulating filminterposed between the electrodes. Then, three subsequent steps areadded to the steps of FIGS. 4A to 4F.

The order in which the steps of FIGS. 4A and 4B are executed may bereversed as long as the transparent storage capacitor electrode EL1 (ST)and the storage capacitor wiring line STG are electrically connected toeach other.

In the first embodiment and the third embodiment described later, athird storage capacitor Cst3 may be formed in a region where thetransparent storage capacitor electrode EL1 (ST), or the storagecapacitor wiring line STG formed in the gate layer, overlaps with thesource electrode S with the gate insulating film INS11 interposedbetween the two by letting the transparent storage capacitor electrodeEL1 (ST) or the storage capacitor wiring line STG slip in under thesource electrode S. In this case, the third storage capacitor Cst3constitutes an equivalent circuit connected in parallel to the firststorage capacitor Cst1 as shown in FIG. 35A.

The sectional structures of the terminal portions and the interlayerconnection portions that are formed by the manufacturing steps of thefirst embodiment are shown in FIGS. 5A to 5D. FIG. 5A shows terminalportions of the scanning line SCN and the storage capacitor wiring lineSTG which are formed in the gate layer. FIG. 5B shows a terminal portionof the signal line SIG which is formed in the drain layer. FIG. 5C showsa connection portion between the common electrode wiring line COM andthe gate layer. FIG. 5D shows a connection portion between the commonelectrode wiring line COM and the drain layer. In FIGS. 5A and 5B, TArepresents a terminal portion as in FIGS. 11A and 11B, FIGS. 14A and14B, FIGS. 17A to 17D, FIGS. 20A and 20B, FIGS. 23A and 23B, FIGS. 26Aand 26B, and FIGS. 29A and 29B, which will be described later.

The transparent electrode EL2 is formed as shown in the drawings inorder to prevent the treatment of the second insulating film INS2 fromdisturbing the gate insulating film INS11 and the passivation film INS12and in order to prevent the treatment of the common electrode wiringline COM from disturbing the gate layer and the drain layer.

The structure of the first embodiment and the structures of the secondto eleventh embodiments described later can also be applied to areflective or transflective liquid crystal display device of IPS displaymode. In that case, a reflective electrode is formed in part of thetransparent storage capacitor electrode EL1 (ST) or part of thetransparent pixel electrode EL2 (P) to be used as a reflective displayportion, which may be provided with a liquid crystal layer thicknessadjusting layer. Using a part of the storage capacitor wiring line STGand a part of the common electrode wiring line COM for the reflectiveelectrode is particularly preferred because it does not increase thenumber of the manufacturing steps.

The structures of those embodiments are also applicable to a liquidcrystal display device that has both, within one pixel, an IPS displaymode transmissive display portion of NB display mode and an IPS displaymode reflective display portion of normally white (NW) display mode.

In this embodiment and all the embodiments described later, thetransparent conductive material employed may be SnO, InZnO, ZnO, or thelike instead of ITO. The transparent storage capacitor electrode EL1(ST), the transparent pixel electrode EL2 (P), and the transparentcounter electrode EL3 (C) are desirably set to thicknesses that areappropriate in terms of manufacture yield and that are appropriate interms of optical design.

The gate layer, the drain layer, and the common electrode wiring lineCOM may also employ Al, Cr, Cu, Mo, Nd, Ta, Ti, W, Zr and other similarmetal materials, or an alloy of those materials.

The gate insulating film INS11, the passivation film INS12, and thesecond insulating film INS2 may be formed from SiO or TaO instead ofSiN, or may also be a laminate of SiO and TaO layers, or may partiallycontain an organic insulating material such as photosensitive acrylicresin.

The gate insulating film INS11, the passivation film INS12, and thesecond insulating film INS2 are desirably set to thicknesses that areappropriate in terms of manufacture yield as well as characteristics andreliability for a thin film transistor TFT and a liquid crystal displaydevice, and that are appropriate in terms of optical design.

The semiconductor layer may be formed from polycrystalline silicon, anorganic semiconductor, crystalline silicon, or the like instead ofamorphous silicon.

The shape in plan view of the transparent counter electrode EL3 (C),which is located closest to the liquid crystal layer LC, may be like aslip or comb-teeth instead of a shape with multiple slit-like openingsSLT which are parallel to one another. The transparent counter electrodeEL3 (C) may also have a shape in plan view that makes it possible togenerate an electric field in multiple different field directions, andhence the liquid crystal layer LC can change to multiple domains havingdifferent alignment directions upon application of an electric field tothe liquid crystal layer LC.

How the layers are treated does not need to be limited to aphotolithography process, and printing, ink jet, or the like may beemployed. The dielectric anisotropy of the liquid crystal compositionmay also be negative, and the liquid crystal composition does not alwaysneed to be a nematic liquid crystal, depending on the display mode.

Second Embodiment

FIGS. 6A and 6B are schematic diagrams showing a pixel structure in aliquid crystal display device according to the second embodiment of thepresent invention. Shown in FIG. 6A is the sectional structure of apixel, and shown in FIG. 6B is the plan view structure of the pixel onthe TFT substrate side. The sectional structure of FIG. 6A correspondsto a view taken along the line A-A′ shown in FIG. 6B.

The difference from the first embodiment is that, instead of using thecommon electrode wiring line COM between the transparent counterelectrode EL3 (C) and the second insulating film INS2, the secondembodiment makes the storage capacitor wiring line STG formed in thegate layer double as the common electrode wiring line COM.

The transparent counter electrode EL3 (C) in the second embodiment isreduced in resistance as in the first embodiment by forming openings(contact holes CH2 to CH4) in a portion of the gate insulating film INS11, a portion of the passivation film INS12, and a portion of the secondinsulating film INS2 that are located above the common electrode wiringline formed in the gate layer, and by connecting the transparent counterelectrode EL3 (C) to the common electrode wiring line COM through theopenings (CH2 to CH4).

An equivalent circuit per pixel in the second embodiment, where thestorage capacitor wiring line STG doubles as the common electrode wiringline COM, is as shown in FIG. 7.

In the second embodiment, an equivalent storage capacitor sufficientlylarge in relation to the parasitic capacitors including Cgs, Cds1, andCds2 can also be formed from the parallel capacitance of the firststorage capacitor Cst1 and the second storage capacitor Cst2, and thesame effects as in the first embodiment can be attained.

In this embodiment and the fourth embodiment described later, a voltagemay be applied commonly to the common electrode wiring line COM in onepixel row and the common electrode wiring line COM in another pixel row,or the common electrode wiring line COM and the transparent counterelectrode EL3 (C) in one pixel row may be separated from those inanother pixel row to receive voltage application independently of theother pixel row.

In FIG. 6B, the openings (CH2 to CH4) are formed in the gate insulatingfilm INS11, the passivation film INS12, and the second insulating filmINS2 as a connection portion between the transparent counter electrodeEL3 (C) and the common electrode wiring line COM. The transparentcounter electrode EL3 (C) accordingly has a smaller region where theslit-like openings SLT are provided to apply an electric field to theliquid crystal layer LC, and the aperture ratio is lowered compared toFIG. 2B. However, the structure of FIG. 6B has an advantage over thestructure of FIG. 2B in that the number of TFT substrate manufacturingsteps in the second embodiment is one step less than in the firstembodiment as described below.

FIGS. 8A to 8G show steps of manufacturing the TFT substrate in theliquid crystal display device according to the second embodiment. FIGS.8A to 8D are the same as FIGS. 4A to 4D described in the firstembodiment.

FIG. 8E is similar to FIG. 4E except that the openings (CH2 and CH3) areformed in a portion of the gate insulating film INS11 and a portion ofthe passivation film INS12 that are located above the common electrodewiring line COM, in addition to forming the opening CH1 in a portion ofthe passivation film INS12 that is located above the source electrode S,by treating the gate insulating film INS11 and the passivation filmINS12 at once.

The step of FIG. 8F is the same as the step of FIG. 4F.

FIG. 8G is similar to FIG. 4G except that, when the second insulatingfilm INS2 is treated, an opening CH4 is formed in a portion of thesecond insulating film INS2 that is within the openings (CH2 and CH3) ofthe gate insulating film INS11 and the passivation film INS12, therebyexposing the surface of the common electrode wiring line COM in the gatelayer. Thereafter, a step corresponding to FIG. 4H is skipped, and afilm is formed from a transparent conductive material such as ITO andtreated by a photolithography process to form the transparent counterelectrode EL3 (C) as the one shown in FIG. 6A.

The transparent counter electrode EL3 (C) and the common electrodewiring line COM are electrically connected to each other through theopenings (CH2 to CH4) in the gate insulating film INS11, the passivationfilm INS12, and the second insulating film INS2.

The TFT substrate is thus manufactured by conducting a photolithographyprocess eight times in total.

As in the first embodiment, the steps of FIGS. 8A to 8F can be adoptedfrom a manufacturing process of an IPS liquid crystal display device inwhich a comb-like pixel electrode (P), or a pixel electrode (P) having aslit, is formed on a planar counter electrode (C) with an interlayerinsulating film interposed between the electrodes. Then, two subsequentsteps are added to the steps of FIGS. 8A to 8F.

As in the first embodiment, the order in which the steps of FIGS. 8A and8B are executed may be reversed as long as the transparent storagecapacitor electrode EL1 (ST) and the common electrode wiring line COMare electrically connected to each other.

In this embodiment and the fourth embodiment described later, a thirdstorage capacitor Cst3 may also be formed in a region where thetransparent storage capacitor electrode EL1 (ST), or the commonelectrode wiring line COM formed in the gate layer, overlaps the sourceelectrode S with the gate insulating film INS11 interposed between thetwo by letting the transparent storage capacitor electrode EL1 (ST) orthe common electrode wiring line COM slip in under the source electrodeS. In this case, the third storage capacitor Cst3 constitutes anequivalent circuit connected in parallel to the first storage capacitorCst1, the second storage capacitor Cst2, and the pixel capacitor Cpx asshown in FIG. 35C.

The sectional structures of terminal portions that are formed by themanufacturing steps of the second embodiment are the same as those inFIGS. 5A and 5B. The sectional structures of interlayer connectionportions that are formed by the manufacturing steps of the secondembodiment are the same as those in FIGS. 5C and 5D except for thefollowing points.

In other words, in the second embodiment where the common electrodewiring line COM between the transparent counter electrode EL3 (C) andthe second insulating film INS2 is not used, the sectional structures ofthe interlayer connection portions do not have the common electrodewiring line COM between the transparent counter electrode EL3 (C) andthe second insulating film INS2 unlike those in FIGS. 5C and 5D.

Third Embodiment

FIGS. 9A and 9B are schematic diagrams showing a pixel structure in aliquid crystal display device according to the third embodiment of thepresent invention. Shown in FIG. 9A is the sectional structure of apixel, and shown in FIG. 9B is the plan view structure of the pixel onthe TFT substrate side. The sectional structure of FIG. 9A correspondsto a view taken along the line A-A′ shown in FIG. 9B.

The difference from the first embodiment is that the third embodimentuses the passivation film INS12 as the second insulating film INS2 bymoving the transparent pixel electrode EL2 (P) to a place between thegate insulating film INS11 and the passivation film INS 12 andconstituting the first insulating film INS1 solely from the gateinsulating film INS11.

Accordingly, this embodiment can reduce one insulating film and, inaddition, can easily form a sufficiently large storage capacitor in apixel having reduced pixel dimensions because the capacitance per unitarea of the first insulating film INS1 which constitutes the firststorage capacitor Cst1 is increased.

In the first embodiment, the source electrode S of the thin filmtransistor TFT and the transparent pixel electrode EL2 (P) are connectedto each other through an opening formed in the passivation film INS 12.In the third embodiment, the source electrode S and the transparentpixel electrode EL2 (P) are electrically connected each other by anoverlapping portion between the two.

With the need to form the opening of the passivation film INS 12 in thepixel region eliminated, the area that can be used to display increasesand the aperture ratio is improved. An equivalent circuit thatrepresents a single pixel in the third embodiment is the same as the onein the first embodiment which is shown in FIG. 3.

In FIG. 9B where only one insulating film is formed between the drainlayer and the common electrode wiring line COM and between the drainlayer and the transparent counter electrode EL3 (C), the parasiticcapacitance between the signal line SIG and the common electrode wiringline COM tends to be larger than the parasitic capacitance of FIG. 2B.However, the structure of FIG. 9B has an advantage over the structure ofFIG. 2B in that the number of TFT substrate manufacturing steps in thethird embodiment is one step less than in the first embodiment asdescribed below.

FIGS. 10A to 10G show steps of manufacturing the TFT substrate in theliquid crystal display device according to the third embodiment. FIGS.10A to 10D are the same as FIGS. 4A to 4D described in the firstembodiment.

In FIG. 10E, a film is formed from a transparent conductive materialsuch as ITO and treated by a photolithography process to form thetransparent pixel electrode EL2 (P). The transparent pixel electrode EL2(P) and the source electrode S are electrically connected to each otherby an overlapping portion between the two (the circled portion indicatedby an arrow A). A region where the transparent storage capacitorelectrode EL1 (ST) and the transparent pixel electrode EL2 (P) overlapeach other with the gate insulating film INS11 interposed between theelectrodes serves as the first storage capacitor Cst1.

In FIG. 10F, the passivation film INS12 is formed from SiN, and the gateinsulating film INS11 and the passivation film INS12 are treated by aphotolithography process at once. By this photolithography process, apixel portion is not patterned, whereas openings are opened in terminalportions and interlayer connection portions.

In FIG. 10G, a film is formed from a metal material and is treated by aphotolithography process to form the common electrode wiring line COM.

Lastly, a film is formed from a transparent conductive material such asITO to cover the common electrode wiring line COM, and is treated by aphotolithography process to form the transparent counter electrode EL3(C) as the one shown in FIG. 9A. The TFT substrate is thus manufacturedby conducting a photolithography process eight times in total.

As in the first embodiment, the order in which the steps of FIGS. 10Aand 10B are executed may be reversed as long as the transparent storagecapacitor electrode EL1 (ST) and the common electrode wiring line COMare electrically connected to each other.

A third storage capacitor Cst3 may also be formed in a region where thetransparent storage capacitor electrode EL1 (ST) and the sourceelectrode S overlap each other with the gate insulating film INS11interposed between the two by letting the transparent storage capacitorelectrode EL1 (ST) slip in under the source electrode S. In this case,the third storage capacitor Cst3 constitutes an equivalent circuit asthe one shown in FIG. 35A.

The connection portion between the transparent pixel electrode EL2 (P)and the source electrode S may also have a structure reverse to the oneshown in FIG. 9A, and hence the source electrode S is laid on top of thetransparent pixel electrode EL2 (P) (see a structure indicated by anarrow F shown in FIG. 9A), because the connection portion is merelyrequired to establish an electric connection between the transparentpixel electrode EL2 (P) and the source electrode S. This structure canbe formed by reversing the order in which the steps of FIG. 10D and FIG.10E are executed.

The sectional structures of the terminal portions and the interlayerconnection portions that are formed by the manufacturing steps of thethird embodiment are shown in FIGS. 11A to 11D. FIG. 11A shows terminalportions of the scanning line SCN and the storage capacitor wiring lineSTG which are formed in the gate layer. FIG. 11B shows a terminalportion of the signal line SIG which is formed in the drain layer. FIG.11C shows a connection portion between the common electrode wiring lineCOM and the gate layer. FIG. 11D shows a connection portion between thecommon electrode wiring line COM and the drain layer.

The common electrode wiring line COM is formed as shown in the drawingsin order to prevent the treatment of the common electrode wiring lineCOM from disturbing the gate layer and the drain layer.

Fourth Embodiment

FIGS. 12A and 12B are schematic diagrams showing a pixel structure in aliquid crystal display device according to the fourth embodiment of thepresent invention. Shown in FIG. 12A is the sectional structure of apixel, and shown in FIG. 12B is the plan view structure of the pixel onthe TFT substrate side. The sectional structure of FIG. 12A correspondsto a view taken along the line A-A′ shown in FIG. 12B.

The difference from the third embodiment is that, instead of using thecommon electrode wiring line COM between the transparent counterelectrode EL3 (C) and the passivation film INS12, the fourth embodimentmakes the storage capacitor wiring line STG formed in the gate layerdouble as the common electrode wiring line COM as in the secondembodiment.

The transparent counter electrode EL3 (C) in the fourth embodiment isreduced in resistance as in the third embodiment by forming openings(contact holes CH1 and CH2) in a portion of the gate insulating film INS11 and a portion of the passivation film INS12 that are located abovethe common electrode wiring line COM formed in the gate layer, and byconnecting the transparent counter electrode EL3 (C) to the commonelectrode wiring line COM through the openings (CH1 and CH2).

An equivalent circuit per pixel in the fourth embodiment, where thestorage capacitor wiring line STG doubles as the common electrode wiringline COM, is the same as the one described in the second embodiment withreference to FIG. 7.

In FIG. 12B, the openings (CH1 and CH2) are formed in the gateinsulating film INS11 and the passivation film INS12 as a connectionportion between the transparent counter electrode EL3 (C) and the commonelectrode wiring line COM. The transparent counter electrode EL3 (C)accordingly has a smaller region where the slit-like openings SLT areprovided to apply an electric field to the liquid crystal layer LC, andthe aperture ratio is lowered compared to FIG. 9B. However, thestructure of FIG. 12B has an advantage over the structure of FIG. 9B inthat the number of TFT substrate manufacturing steps in the fourthembodiment is even smaller (by one step) than in the third embodiment asdescribed below.

FIGS. 13A to 13F show steps of manufacturing the TFT substrate in theliquid crystal display device according to the fourth embodiment. FIGS.13A to 13E are the same as FIGS. 10A to 10E described in the thirdembodiment.

FIG. 13F is similar to FIG. 10F except that the openings (CH1 and CH2)are formed in a portion of the gate insulating film INS11 and a portionof the passivation film INS12 that are located above the commonelectrode wiring line COM, in addition to forming openings in terminalportions and interlayer connection portions, by treating the gateinsulating film INS11 and the passivation film INS12 at once, thusexposing the surface of the common electrode wiring line COM formed inthe gate layer.

Thereafter, a step corresponding to FIG. 10G is skipped, and a film isformed from a transparent conductive material such as ITO and treated bya photolithography process to form the transparent counter electrode EL3(C) as the one shown in FIG. 12A. The transparent counter electrode EL3(C) and the common electrode wiring line COM are electrically connectedto each other through the openings (CH1 and CH2) in the gate insulatingfilm INS11 and the passivation film INS12. The TFT substrate is thusmanufactured by conducting a photolithography process seven times intotal.

As in the third embodiment, the order in which the steps of FIGS. 13Aand 13B are executed may be reversed as long as the transparent storagecapacitor electrode EL1 (ST) and the common electrode wiring line COMare electrically connected to each other.

A third storage capacitor Cst3 may also be formed in a region where thetransparent storage capacitor electrode EL1 (ST) and the sourceelectrode S overlap each other with the gate insulating film INS11interposed between the two by letting the transparent storage capacitorelectrode EL1 (ST) slip in under the source electrode S. In this case,the third storage capacitor Cst3 constitutes an equivalent circuit asthe one shown in FIG. 35C.

As is the case for the connection portion between the transparent pixelelectrode EL2 (P) and the source electrode S in the third embodiment,the connection portion between the transparent pixel electrode EL2 (P)and the source electrode S in the fourth embodiment may also have astructure reverse to the one shown in FIG. 12A, and hence the sourceelectrode S is laid on top of the transparent pixel electrode EL2 (P),because the connection portion is merely required to establish anelectric connection between the transparent pixel electrode EL2 (P) andthe source electrode S. This structure can be formed by reversing theorder in which the steps of FIG. 13D and FIG. 13E are executed.

The sectional structures of the terminal portions and the interlayerconnection portions that are formed by the manufacturing steps of thefourth embodiment are shown in FIGS. 14A to 14D. In the fourthembodiment where the common electrode wiring line COM between thetransparent counter electrode EL3 (C) and the passivation film INS12 isnot used, the sectional structures of the terminal portions and theinterlayer connection portions do not have the common electrode wiringline COM between the transparent counter electrode EL3 (C) and thepassivation film INS12 unlike those in FIGS. 11A to 11D.

Fifth Embodiment

In the first to fourth embodiments, limitations are put on the materialand thickness of the gate insulating film and the passivation film inconsideration of the characteristics and reliability of the thin filmtransistor TFT, and an insulating film used for a storage capacitor isalso bound by the limitations. In the fifth embodiment and the sixthembodiment described later, the first and second storage capacitors aremoved to a layer above the passivation film and are each formed from adedicated insulating film, thereby increasing the degree of freedom inselecting a material, a thickness, and the like for the first and secondinsulating films used for storage capacitors.

FIGS. 15A and 15B are schematic diagrams showing a pixel structure in aliquid crystal display device according to the fifth embodiment of thepresent invention. Shown in FIG. 15A is the sectional structure of apixel, and shown in FIG. 15B is the plan view structure of the pixel onthe TFT substrate side. The sectional structure of FIG. 15A correspondsto a view taken along the line A-A′ shown in FIG. 15B.

On a first substrate SUB1, signal lines SIG are formed to intersect withscanning lines SCN with a gate insulating film INS11 interposedtherebetween. Each pixel defined by the intersecting scanning lines SCNand signal lines SIG is provided with a thin film transistor TFT and atransparent pixel electrode EL2 (P), which functions as the secondtransparent electrode.

As shown in FIG. 15A, a transparent storage capacitor electrode EL1(ST), which functions as a first transparent electrode, is formedbetween a passivation film INS12 of the thin film transistor TFT and afirst insulating film INS1. An opening (contact hole) CH1 is formed inthe passivation film INS12 to electrically connect the transparent pixelelectrode EL2 (P) and a source electrode S of the thin film transistorTFT to each other. The transparent storage capacitor electrode EL1 (ST)has an opening SPK, which is apart from the opening CH1 by at least aminimum insulation distance.

The transparent storage capacitor electrode EL1 (ST) in one pixel may beseparated from the transparent storage capacitor electrode EL1 (ST) inanother pixel. Desirably, the transparent storage capacitor electrodesEL1 (ST) in adjacent pixels are connected to each other in order thatthe resistance can be lowered. The laminate composed of the gateinsulating film INS11 and the passivation film INS12 below thetransparent storage capacitor electrode EL1 (ST) constitutes a thirdinsulating film INS3.

A common electrode wiring line COM which is shaped after the shape ofthe scanning line SCN and the signal line SIG and which doubles as astorage capacitor wiring line STG is formed on the transparent storagecapacitor electrode EL1 (ST). A first storage capacitor Cst1 is formedbetween the transparent storage capacitor electrode EL1 (ST) and thetransparent pixel electrode EL2 (P) through a first insulating filmINS1.

A second insulating film INS2 and a transparent counter electrode EL3(C), which functions as a third transparent electrode, are formed abovethe transparent pixel electrode EL2 (P). At this point, openings(contact holes CH3 and CH4) are formed in a portion of the firstinsulating film INS1 and a portion of the second insulating film INS2that are located above the common electrode wiring line COM. Thetransparent counter electrode EL3 (C) and the common electrode wiringline COM are connected to each other through the openings (CH3 and CH4).The overall resistance of the counter electrode is thus lowered.

Multiple slit-like openings SLT parallel to one another are formed inthe transparent counter electrode EL3 (C), avoiding the connectionportion between the transparent counter electrode EL3 (C) and the commonelectrode wiring line COM.

A second storage capacitor Cst2 is formed between the transparent pixelelectrode EL2 (P) and the transparent counter electrode EL3 (C) throughthe second insulating film INS2 to thereby obtain the TFT substrate. Afirst alignment film AL1 for aligning a liquid crystal layer LC in agiven direction is formed in the topmost layer of the TFT substrate.

On a second substrate SUB2, a light shielding film (black matrix) BM, acolor filter FIL whose color varies from one pixel to another, aprotective film (overcoat) OC, and a second alignment film AL2 areformed to obtain a counter substrate.

The first alignment film AL1 and the second alignment film AL2 are eachprocessed in advance so that liquid crystal molecules are aligned in agiven direction. The first substrate SUB1 and the second substrate SUB2are arranged such that their alignment film formation faces are opposedto each other across a predetermined interval, and the gap between thetwo is filled with a nematic liquid crystal composition having apositive dielectric anisotropy to form the liquid crystal layer LC.

The transparent pixel electrode EL2 (P) and the transparent counterelectrode EL3 (C) are arranged such that an electric field having acomponent parallel to the surface of the first substrate SUB1 isgenerated between the transparent pixel electrode EL2 (P) and thetransparent counter electrode EL3 (C) through the liquid crystal layerLC to form a pixel capacitor Cpx.

A retardation plate and polarization plate (not shown) are disposedoutside of the first substrate SUB1 and the second substrate SUB2 toobtain an NB display mode liquid crystal display device. Drive circuits(not shown) are connected to the scanning lines SCN, the signal linesSIG, and the common electrode wiring lines COM.

An equivalent circuit that represents a single pixel in the liquidcrystal display device according to the fifth embodiment and in a liquidcrystal display device according to the sixth embodiment which will bedescribed later is the same as the one described in the secondembodiment with reference to FIG. 7.

In the fifth embodiment and the sixth embodiment described later, thetransparent storage capacitor electrode EL1 (ST), the common electrodewiring line COM, and the transparent counter electrode EL3 (C) in onepixel row may be separated from those in another pixel row to receivevoltage application independently of those in the other pixel row, orthe transparent storage capacitor electrode EL1 (ST), the commonelectrode wiring line COM, and the transparent counter electrode EL3 (C)in one pixel column may be separated from those in another pixel columnto receive voltage application independently of those in the other pixelcolumn, although, from the standpoint of reducing the resistance of thecounter electrode, it is preferred to connect the transparent storagecapacitor electrode EL1 (ST), the common electrode wiring line COM, andthe transparent counter electrode EL3 (C) in one pixel to those inadjacent pixels so that a voltage is applied commonly to all pixels.

In the fifth embodiment and the sixth embodiment described later, athird storage capacitor Cst3 may be formed between a source electrode Sand the capacitor storage wiring line STG through the gate insulatingfilm INS11 by forming the storage capacitor wiring line STG in a gatelayer below the source electrode S. In this case, the third storagecapacitor Cst3 constitutes an equivalent circuit as the one shown inFIG. 35B.

FIGS. 16A to 16H show steps of manufacturing the TFT substrate in theliquid crystal display device according to the fifth embodiment.

In FIG. 16A, a film is formed from a metal material on the firstsubstrate SUB1, which is a transparent insulating member such as a glasssubstrate. The film is treated by a photolithography process to form agate electrode G and the scanning line SCN (not shown). This layer iscalled a gate layer.

In FIG. 16B, the gate insulating film INS11, which is made of atransparent insulating material such as SiN, SiO, or TaO, and asemiconductor layer a-Si, which is made of amorphous silicon, are formedin succession, and only the semiconductor layer a-Si is treated by aphotolithography process. A heavily doped n-type thin film (not shown)is present on the top face of the semiconductor layer a-Si.

In FIG. 16C, a film is formed from a metal material to form the sourceelectrode S, a drain electrode D, and the signal line SIG (not shown)simultaneously by a photolithography process. This layer is called adrain layer. The heavily doped n-type layer which is not covered withthe drain layer is removed at the same time when the drain layer istreated.

In FIG. 16D, the passivation film INS12 is formed from SiN. While thepassivation film INS12 is left untreated, a film is formed from atransparent conductive material such as ITO on the passivation filmINS12 and is treated by a photolithography process to form thetransparent storage capacitor electrode EL1 (ST).

In FIG. 16E, a film is formed from a metal material and is treated by aphotolithography process to form the common electrode wiring line COM.

In FIG. 16F, the first insulating film INS1 is formed from SiN, andthen, three layers, the gate insulating film INS11, the passivation filmINS12, and the first insulating film INS1, are treated by aphotolithography process at once.

Openings (CH1 and CH2) are formed in a portion of the passivation filmINS12 and a portion of the first insulating film INS1 that are locatedabove the source electrode S, and the opening CH3 is formed in a portionof the first insulating film INS1 that is located above the commonelectrode wiring line COM to expose the surface of the common electrodewiring line COM.

In FIG. 16G, a film is formed from a transparent conductive materialsuch as ITO and is treated by a photolithography process to form thetransparent pixel electrode EL2 (P).

The transparent pixel electrode EL2 (P) is electrically connected to thesource electrode S through the openings (CH1 and CH2) in the passivationfilm INS12 and the first insulating film INS1. However, the transparentpixel electrode EL2 (P) is removed from inside the opening CH3 in thefirst insulating film INS1 which is located above the common electrodewiring line COM, and from around the opening CH3 for at least a minimuminsulation distance.

In FIG. 16H, the second insulating film INS2 is formed from SiN and istreated by a photolithography process. Through this photolithographyprocess, the opening CH4 is formed in the second insulating film INS2 ina portion where the opening CH3 has been formed in the first insulatingfilm INS1 above the common electrode wiring line COM, thereby exposingthe surface of the common electrode wiring line COM again.

Lastly, a film is formed from a transparent conductive material such asITO and is treated by a photolithography process to form the transparentcounter electrode EL3 (C) as the one shown in FIG. 15A.

The transparent counter electrode EL3 (C) is electrically connected tothe common electrode wiring line COM through the openings (CH3 and CH4)in the first insulating film INS1 and the second insulating film INS2.The TFT substrate is thus manufactured by conducting a photolithographyprocess nine times in total.

Compared to the first embodiment, one more insulating film is formed inthis embodiment by conducting a photolithography process as many timesas in the first embodiment. The fifth embodiment can thus increase thedegree of freedom in selecting a material, a thickness, and the like forthe first and second insulating films through which storage capacitorsare formed without adding many steps to the manufacturing process of thefirst embodiment.

The sectional structures of terminal portions and interlayer connectionportions that are formed by the manufacturing steps of the fifthembodiment are shown in FIGS. 17A to 17F.

FIG. 17A shows a terminal portion of the scanning line SCN formed in thegate layer. FIG. 17C shows a terminal portion of the signal line SIGformed in the drain layer. FIG. 17E shows a connection portion betweenthe common electrode wiring line COM and the gate layer. FIG. 17F showsa connection portion between the common electrode wiring line COM andthe drain layer.

In order to prevent the treatment of the second insulating film INS2from disturbing the gate insulating film INS11, the passivation filmINS12, and the first insulating film INS1, the opening in the secondinsulating film INS2 is shaped such that the surrounding areas of theopenings formed by treating the three layers, the gate insulating filmINS11, the passivation film INS12, and the first insulating film INS1,at once are covered.

The layer of the common electrode wiring line COM or the layer of thetransparent electrode EL1 cannot be connected directly to the gate layerand the drain layer. Therefore, as shown in FIGS. 17E and 17F, the layerof the transparent electrode EL3 is connected to the common electrodewiring line COM through the openings formed in a portion of the firstinsulating film INS1 and a portion of the second insulating film INS2that are located above the common electrode wiring line COM, and thecommon electrode wiring line COM is connected to the gate layer and thedrain layer through this layer of the transparent electrode EL3.

FIG. 17B is a modification example of FIG. 17A, and FIG. 17D is amodification example of FIG. 17C. Forming the layer of the transparentelectrode EL2 in the manner shown in the drawings prevents the treatmentof the second insulating film INS2 from disturbing the gate insulatingfilm INS11, the passivation film INS12, and the first insulating filmINS1, and allows the second insulating film INS2 to have a largeropening. Those structures are therefore effective particularly whenterminals are aligned at a small pitch.

Sixth Embodiment

FIGS. 18A and 18B are schematic diagrams showing a pixel structure in aliquid crystal display device according to the sixth embodiment of thepresent invention. FIG. 18A shows the sectional structure of a pixel andFIG. 18B shows the plan view structure of the pixel on the TFT substrateside. The sectional structure shown in FIG. 18A corresponds to a viewtaken along the line A-A′ illustrated in FIG. 18B.

The sixth embodiment is a modification example of the fifth embodiment,and differs from the fifth embodiment described with reference to FIGS.15A and 15B in the following points.

The common electrode wiring line COM is placed below the transparentcounter electrode EL3 (C) instead of above the transparent storagecapacitor electrode EL1 (ST). This modification is accompanied by achange in structure of the opening through which the transparent storagecapacitor electrode EL1 (ST) and the transparent counter electrode EL3(C) are electrically connected to each other.

Specifically, in the opening CH3 formed in a portion of the firstinsulating film INS1 that is located above the transparent storagecapacitor electrode EL1 (ST), an insular transparent electrode patternEL2′ separated from the transparent pixel electrode EL2 (P) is formedfrom the layer of the transparent pixel electrode EL2 (P). The insulartransparent electrode pattern EL2′ is connected to the transparentstorage capacitor electrode EL1 (ST), and then connected to the commonelectrode wiring line COM through the opening CH4 formed in a portion ofthe second insulating film INS2 that is located above the insulartransparent electrode pattern EL2′.

The common electrode wiring line COM is not always necessary in theopening CH4 formed in a portion of the second insulating film INS2 thatis located above the insular transparent electrode pattern EL2′.Accordingly, the transparent counter electrode EL3 (C) may be formeddirectly in the opening CH4 within the second insulating film INS2 abovethe insular transparent electrode pattern EL2′.

In the sixth embodiment, the insular transparent electrode pattern EL2′whose voltage is as high as the voltage of the common electrode wiringline COM needs to be electrically insulated from the transparent pixelelectrode EL2 (P) despite the two being the same layer, and thereforemust be distanced from the transparent pixel electrode EL2 (P) as shownin FIG. 18B. The required distance makes the transparent pixel electrodeEL2 (P) in the sixth embodiment that much smaller in area than in thefifth embodiment. The transparent counter electrode EL3 (C) accordinglyhas a smaller region where the slit-like openings SLT are provided toapply an electric field to the liquid crystal layer LC, and the apertureratio is lowered compared to the fifth embodiment. However, the sixthembodiment has the following advantage over the fifth embodiment.

If the common electrode wiring line COM formed from a non-transparentmetal material is shaped so as to overlap with the scanning line SCN andthe signal line SIG in the fifth embodiment, it leaves the passivationfilm INS12 as the only insulating film between the drain layer and thecommon electrode wiring line COM and between the drain layer and thetransparent storage capacitor electrode EL1 (ST). The capacitance of theparasitic capacitor between the signal line SIG and the common electrodewiring line COM is likely to increase as a result.

In contrast, the parasitic capacitor between the signal line SIG and thecommon electrode wiring line COM can be smaller in the sixth embodimentwhere the insulating film between the drain layer and the commonelectrode wiring line COM and between the drain layer and thetransparent storage capacitor electrode EL1 (ST) is a laminateconstituted of the passivation film INS12, the first insulating filmINS1, and the second insulating film INS2, which makes the capacitanceper-unit area small.

FIGS. 19A to 19H show steps of manufacturing the TFT substrate in theliquid crystal display device according to the sixth embodiment. FIGS.19A to 19D are the same as FIGS. 16A to 16D in the fifth embodiment,except for the shape of the transparent storage capacitor electrode EL1(ST).

In FIG. 19E, the first insulating film INS1 is formed from SiN, and thenthree layers, the gate insulating film INS11, the passivation filmINS12, and the first insulating film INS1, are treated by aphotolithography process at once. Openings (CH1 and CH2) are formed in aportion of the passivation film INS12 and a portion of the firstinsulating film INS1 that are located above the source electrode S, andthe opening CH3 is formed in a portion of the first insulating film INS1that is located above the transparent storage capacitor electrode EL1(ST) to expose the surface of the transparent storage capacitorelectrode EL1 (ST).

In FIG. 19F, a film is formed from a transparent conductive materialsuch as ITO and is treated by a photolithography process to form thetransparent pixel electrode EL2 (P) and the insular transparentelectrode pattern EL2′. The transparent pixel electrode EL2 (P) iselectrically connected to the source electrode S through the openings(CH1 and CH2) in the passivation film INS12 and the first insulatingfilm INS1. The insular transparent electrode pattern EL2′ iselectrically connected to the transparent storage capacitor electrodeEL1 (ST) through the opening CH3 in the first insulating film INS1.

In FIG. 19G, the second insulating film INS2 is formed from SiN and istreated by a photolithography process. Through this photolithographyprocess, the opening CH4 is formed in a portion of the second insulatingfilm INS2 that is located above the insular transparent electrodepattern EL2′, thereby exposing the surface of the insular transparentelectrode pattern EL2′.

In FIG. 19H, a film is formed from a metal material and is treated by aphotolithography process to form the common electrode wiring line COM.The common electrode wiring line COM is electrically connected to theinsular transparent electrode pattern EL2′ through the opening CH4 inthe second insulating film INS2.

Lastly, a film is formed from a transparent conductive material such asITO, covering the common electrode wiring line COM, and is treated by aphotolithography process to form the transparent counter electrode EL3(C) as the one shown in FIG. 18A. The TFT substrate is thus manufacturedby conducting a photolithography process nine times in total. In thisway, the sixth embodiment can increase the degree of freedom inselecting a material, a thickness, and the like for the first and secondinsulating films through which storage capacitors are formed withoutadding to the number of manufacturing process steps of the fifthembodiment.

The sectional structures of terminal portions and interlayer connectionportions that are formed by the manufacturing steps of the sixthembodiment are shown in FIGS. 20A to 20D. FIG. 20A shows a terminalportion of the scanning line SCN formed in the gate layer. FIG. 20Bshows a terminal portion of the signal line SIG formed in the drainlayer. The terminal portion structures of the sixth embodiment shown inFIGS. 20A and 20B are the same as those of the fifth embodiment shown inFIGS. 17B and 17D, respectively.

FIG. 20C shows a connection portion between the common electrode wiringline COM and the gate layer. FIG. 20D shows a connection portion betweenthe common electrode wiring line COM and the drain layer. Thetransparent electrode EL2 is formed as shown in the drawings in order toprevent the treatment of the second insulating film INS2 from disturbingthe gate insulating film INS11, the passivation film INS12, and thefirst insulating film INS1, and in order to prevent the treatment of thecommon electrode wiring line COM from disturbing the gate layer and thedrain layer.

Seventh Embodiment

The seventh embodiment, as well as the eighth to tenth embodiments whichwill be described later, presents an example of an IPS liquid crystaldisplay device that is structured such that a first transparentelectrode EL1 and a third transparent electrode EL3 are used as pixelelectrodes P, whereas a second transparent electrode EL2 is used as acounter electrode C that doubles as a storage capacitor electrode.

FIGS. 21A and 21B are schematic diagrams showing a pixel structure inthe liquid crystal display device according to the seventh embodiment ofthe present invention. FIG. 21A shows the sectional structure of a pixeland FIG. 21B shows the plan view structure of the pixel on the TFTsubstrate side. The sectional structure shown in FIG. 21A corresponds toa view taken along the line A-A′ illustrated in FIG. 21B.

On a first substrate SUB1, signal lines SIG are formed to intersect withscanning lines SCN with a gate insulating film INS11 interposedtherebetween. Each pixel defined by the intersecting scanning lines SCNand signal lines SIG is provided with a thin film transistor TFT, afirst transparent pixel electrode EL1 (P), which functions as the firsttransparent electrode and is shaped like a flat board, and a secondtransparent pixel electrode EL3 (P), which functions as the thirdtransparent electrode.

The second transparent pixel electrode EL3 (P) has a planar shape withslit-like openings SLT which run parallel to one another. Alternatively,the second transparent pixel electrode EL3 (P) may have a planar shapelike a slip or a comb.

The first transparent pixel electrode EL1 (P) between the gateinsulating film INS11 and a passivation film INS12 is electricallyconnected to a source electrode S of the thin film transistor TFT by anoverlapping portion between the first transparent pixel electrode EL1(P) and the source electrode S.

The second transparent pixel electrode EL3 (P) which is above a secondinsulating film INS2 is electrically connected to the source electrode Sthrough openings (CH1 and CH2) formed in a portion of the passivationfilm INS12 and a portion of the second insulating film INS2 that arelocated above the source electrode S.

A transparent counter electrode EL2 (C), which functions as the secondtransparent electrode and doubles as a storage capacitor electrode, isformed between the second insulating film INS2 and the passivation filmINS12. The transparent counter electrode EL2 (C) has an opening SPKdistanced from the openings CH1 and CH2, which are formed in thepassivation film INS12 and the second insulating film INS2 toelectrically connect the second transparent pixel electrode EL3 (P) andthe source electrode S to each other, by at least a minimum insulationdistance. The passivation film INS12 is used as a first insulating filmINS1 through which a first storage capacitor Cst1 is formed between thefirst transparent pixel electrode EL1 (P) and the transparent counterelectrode EL2 (C). A second storage capacitor Cst2 is formed between thetransparent counter electrode EL2 (C) and the second transparent pixelelectrode EL3 (P) through the second insulating film INS2. The gateinsulating film INS11 constitutes a third insulating film INS3.

A common electrode wiring line COM which is shaped after the shape ofthe scanning line SCN and the signal line SIG and which doubles as astorage capacitor wiring line STG is formed between the passivation filmINS12 and the transparent counter electrode EL2 (C). The transparentcounter electrode EL2 (C) and the common electrode wiring line COMdirectly overlap each other to be electrically connected to each otherand thereby lower the overall resistance of the counter electrode. Afirst alignment film AL1 for aligning a liquid crystal layer LC in agiven direction is formed in the topmost layer of the TFT substrate.

On a second substrate SUB2, a light shielding film (black matrix) BM, acolor filter FIL whose color varies from one pixel to another, aprotective film (overcoat) OC, and a second alignment film AL2 areformed to obtain a counter substrate.

The first alignment film AL1 and the second alignment film AL2 are eachprocessed in advance so that liquid crystal molecules are aligned in agiven direction.

The first substrate SUB1 and the second substrate SUB2 are arranged suchthat their alignment film formation faces are opposed to each otheracross a predetermined interval, and the gap between the two is filledwith a nematic liquid crystal composition having a positive dielectricanisotropy to form the liquid crystal layer LC.

The seventh embodiment employs an IPS method electrode arrangement inwhich an electric field having a component parallel to the surface ofthe first substrate SUB1 is generated between the transparent counterelectrode EL2 (C) and the second transparent pixel electrode EL3 (P)through the liquid crystal layer LC to form a pixel capacitor Cpx.

A retardation plate and polarization plate (not shown) are disposedoutside of the first substrate SUB1 and the second substrate SUB2 toobtain an NB display mode liquid crystal display device. Drive circuits(not shown) are connected to the scanning lines SCN, the signal linesSIG, and the common electrode wiring lines COM.

An equivalent circuit that represents a single pixel in the liquidcrystal display device according to the seventh embodiment is the sameas the one described in the second embodiment with reference to FIG. 7.

The first transparent pixel electrode EL1 (P), the second transparentpixel electrode EL3 (P), or the source electrode S is provided with aparasitic capacitor Cgs, which is formed between the gate (G) and source(S) of the thin film transistor TFT, and parasitic capacitors Cds1 andCds2, which are formed by the electrode EL1, EL3, or S and the signallines SIG, in addition to the first storage capacitor Cst1, the secondstorage capacitor Cst2, and the pixel capacitor Cpx.

When the pixel dimensions are reduced to obtain fine pixels, anequivalent storage capacitor sufficiently large in relation to theparasitic capacitors including Cgs, Cds1, and Cds2 can be formed fromthe parallel capacitance of the first storage capacitor Cst1 and thesecond storage capacitor Cst2.

This makes the voltage of the second transparent pixel electrode EL3 (P)less susceptible to feed-through voltage, which is caused by a voltagechange in the scanning line SCN or the signal line SIG, during a holdperiod in which the thin film transistor TFT is off. Phenomena calledsmearing and cross talk can thus be prevented.

It also reduces the leakage of accumulated electric charges from thefirst transparent pixel electrode EL1 (P), the second transparent pixelelectrode EL3 (P), and the source electrode (S) during a hold period,thereby allowing the electric field applied to the liquid crystal layerLC to drop less.

Accordingly, degradation in image quality can be avoided. Furthermore,since the first storage capacitor Cst1 and the second storage capacitorCst2 are constituted of the first transparent pixel electrode EL1 (P),the passivation film INS12, the transparent counter electrode EL2 (C),the second insulating film INS2, and the second transparent pixelelectrode EL3 (P), which are all transparent, forming a storagecapacitor that is sufficiently large in relation to the parasiticcapacitor does not lower the aperture ratio of the transmissive displayportion. The formation of a sufficiently large storage capacitor and thesecuring of a sufficiently high aperture ratio are thus accomplishedsimultaneously. Those effects of the seventh embodiment are shared bythe eighth to twelfth embodiment which will be described later.

In the seventh embodiment and the eighth to tenth embodiments describedlater, the common electrode wiring line COM and the transparent counterelectrode EL2 (C) in one pixel row may receive voltage applicationindependently of those in another pixel row, or the common electrodewiring line COM and the transparent counter electrode EL2 (C) in onepixel column may receive voltage application independently of those inanother pixel column, although, from the viewpoint of reducing theresistance of the counter electrode, it is preferred to connect thecommon electrode wiring line COM and the transparent counter electrodeEL2 (C) in one pixel to those in adjacent pixels so that a voltage isapplied commonly to all pixels.

In the seventh embodiment and the eighth to tenth embodiments describedlater, a third storage capacitor Cst3 may be formed between the sourceelectrode S and the storage capacitor wiring line STG through the gateinsulating film INS11 by forming the storage capacitor wiring line STGin the gate layer below the source electrode S.

The third storage capacitor Cst3 in this case constitutes an equivalentcircuit as the one shown in FIG. 35B. Besides, the third storagecapacitor Cst3 in the seventh embodiment and the ninth embodimentdescribed later may be formed by placing the storage capacitor wiringline STG below the first transparent pixel electrode EL1 (P) in additionto below the source electrode S, although it lowers the aperture ratioand is not so preferred.

In this case, a voltage may be applied to the storage capacitor wiringline STG commonly to all pixels, or individually on a pixel row basis.Further, the voltage of the storage capacitor wiring line STG and thevoltage of the common electrode wiring line COM may be the same, whichdoes not mean that the two always need to match.

FIGS. 22A to 22G show steps of manufacturing the TFT substrate in theliquid crystal display device according to the seventh embodiment.

In FIG. 22A, a film is formed from a metal material on the firstsubstrate SUB1, which is a transparent insulating member such as a glasssubstrate. The film is treated by a photolithography process to form thegate electrode G and the scanning line SCN (not shown). This layer iscalled a gate layer.

In FIG. 22B, the gate insulating film INS11, which is made of atransparent insulating material such as SiN, SiO, or TaO, and asemiconductor layer a-Si, which is made of amorphous silicon, are formedin succession, and only the semiconductor layer a-Si is treated by aphotolithography process. A heavily doped n-type thin film (not shown)is present on the top face of the semiconductor layer a-Si.

In FIG. 22C, a film is formed from a metal material to form the sourceelectrode S, the drain electrode D, and the signal line SIG (not shown)simultaneously by a photolithography process. This layer is called adrain layer. The heavily doped n-type layer which is not covered withthe drain layer is removed at the same time when the drain layer istreated.

In FIG. 22D, a film is formed from a transparent conductive materialsuch as ITO, and is treated by a photolithography process to form thefirst transparent pixel electrode EL1 (P). The first transparent pixelelectrode EL1 (P) and the source electrode S are electrically connectedto each other by an overlapping portion between the two (the circledportion indicated by an arrow A).

In FIG. 22E, the passivation film INS12 is formed from SiN. While thepassivation film INS12 is left untreated, a film is formed from a metalmaterial on the passivation film INS12 and is treated by aphotolithography process to form the common electrode wiring line COM.

In FIG. 22F, a film is formed from a transparent conductive materialsuch as ITO and is treated by a photolithography process to form thetransparent counter electrode EL2 (C).

In FIG. 22G, the second insulating film INS2 is formed from SiN, andthen three layers, the gate insulating film INS11, the passivation filmINS12, and the second insulating film INS2, are treated by aphotolithography process at once to form openings (CH1 and CH2) in aportion of the passivation film INS12 and a portion of the secondinsulating film INS2 that are located above the source electrode S.

Lastly, a film is formed from a transparent conductive material such asITO, and is treated by a photolithography process to form the secondtransparent pixel electrode EL3 (P) as the one shown in FIG. 21A.

The second transparent electrode EL3 (P) is electrically connected tothe source electrode S through the openings (CH1 and CH2) in the portionof the passivation film INS12 and the portion of the second insulatingfilm INS2 that are located above the source electrode S. The TFTsubstrate is thus manufactured by conducting a photolithography processeight times in total.

While the number of times a photolithography process is conducted in theseventh embodiment is the same as in the second embodiment, the seventhembodiment has the following advantages over the second embodiment.

The seventh embodiment does not need an opening in an insulating film toconnect the common electrode and the counter electrode to each other.The area that can be used to display therefore increases, which makes iteasy to improve the aperture ratio.

The common electrode wiring line COM of the seventh embodiment is in alayer above the passivation film INS12 instead of the gate layer. Theaperture ratio can therefore be improved by utilizing the commonelectrode wiring line COM as a self-shield against light.

The first insulating film INS1 constituting the first storage capacitorCst1 consists solely of the passivation film INS12 in the seventhembodiment, which increases the capacitance per unit area. Accordingly,a sufficiently large storage capacitor can easily be formed in a pixelof smaller dimensions.

The seventh embodiment, where a photolithography process is conducted asmany times as in the third embodiment, has the following advantage overthe third embodiment.

The gate insulating film INS11 in the seventh embodiment is not used asan insulating film for a storage capacitor, which reduces limitationsput on the material and thickness in consideration of thecharacteristics and reliability of the thin film transistor TFT. Theseventh embodiment can thus increase the degree of freedom in selectinga material, a thickness, and the like for the second insulating filmthrough which storage capacitors are formed.

As in the third and fourth embodiments, it is sufficient for theconnection portion between the pixel electrode and the source electrodeS in the seventh embodiment to electrically connect the two. Theconnection portion therefore may have a structure reverse to the oneshown in FIG. 21A, and hence the source electrode S is laid on top ofthe first transparent pixel electrode EL1 (P) (see a structure indicatedby an arrow F in FIG. 21A). This structure can be formed by reversingthe order in which the steps of FIG. 22C and FIG. 22D are executed.

In the seventh embodiment, as well as the eighth to tenth embodiments,part of the eleventh embodiment, and the twelfth embodiment which willbe described later, the transparent counter electrode EL2 (C) and thecommon electrode wiring line COM may be arranged otherwise as long asthe two are electrically connected to each other. Therefore, thesectional structures of the pixel portions of the respective embodimentsshown in the schematic diagrams may be reversed, and hence the commonelectrode wiring line COM is laid on top of the transparent counterelectrode EL2 (C).

This structure is obtained by switching the order of the formation andtreatment step of the transparent counter electrode EL2 (C) and theformation and treatment step of the common electrode wiring line COM inthe TFT manufacturing processes of the respective embodiments shown inthe drawings.

The sectional structures of terminal portions and interlayer connectionportions that are formed by the manufacturing steps of the seventhembodiment, and of the tenth embodiment described later, are shown inFIGS. 23A to 23D. FIG. 23A shows a terminal portion of the scanning lineSCN formed in the gate layer. FIG. 23B shows a terminal portion of thesignal line SIG formed in the drain layer. FIG. 23C shows a connectionportion between the common electrode wiring line COM and the gate layer.FIG. 23D shows a connection portion between the common electrode wiringline COM and the drain layer.

The terminal portions only need the transparent electrode EL3 becausethe layer of the second transparent pixel electrode EL3 (P) is formedimmediately after the gate insulating film INS11, the passivation filmINS12, and the second insulating film INS2 are treated at once.

However, since the common electrode wiring line COM or the transparentcounter electrode EL2 (C) cannot be connected directly to the gate layeror the drain layer, the layer of the transparent electrode EL3 isconnected to the common electrode wiring line COM through an opening ina portion of the second insulating film INS2 that is located above thetransparent counter electrode EL2 (C), and the common electrode wiringline COM is connected to the gate layer and the drain layer through thislayer of the transparent electrode EL3.

Eighth Embodiment

FIGS. 24A and 24B are schematic diagrams showing a pixel structure in aliquid crystal display device according to the eighth embodiment of thepresent invention. FIG. 24A shows the sectional structure of a pixel andFIG. 24B shows the plan view structure of the pixel on the TFT substrateside. The sectional structure shown in FIG. 24A corresponds to a viewtaken along the line A-A′ illustrated in FIG. 24B.

The eighth embodiment is a modification example of the seventhembodiment, and differs from the seventh embodiment described withreference to FIGS. 21A and 21B in the following points.

The first transparent pixel electrode EL1 (P) is placed between thefirst substrate SUB1 and the gate insulating film INS11 instead ofbetween the gate insulating film INS11 and the passivation film INS12,and a laminate constituted of the gate insulating film INS11 and thepassivation film INS12 is used as the first insulating film INS1.

To accommodate this modification, the opening CH1 for electricallyconnecting the source electrode S of the thin film transistor TFT andthe first transparent pixel electrode EL1 (P) to each other is formed ina portion of the gate insulating film INS11 that is located below thesource electrode S.

The first insulating film INS1 and the second insulating film INS2 whichare used for the first storage capacitor Cst1 and the second storagecapacitor Cst2 respectively are thus given the same structures as in thefirst embodiment and the second embodiment.

The eighth embodiment differs from the first and second embodiments inthat the first transparent pixel electrode EL1 (P) and the secondtransparent pixel electrode EL3 (P) serve as pixel electrodes P, whereasthe transparent counter electrode EL2 (C) doubles as a counter electrodeC and a storage capacitor electrode. An equivalent circuit thatrepresents a single pixel in the eighth embodiment is the same as theone described in the second embodiment with reference to FIG. 7.

FIGS. 25A to 25H show steps of manufacturing the TFT substrate in theliquid crystal display device according to the eighth embodiment. FIGS.25A to 25C are the same as FIGS. 4A to 4C described in the firstembodiment and FIGS. 8A to 8C described in the second embodiment, exceptthat the storage capacitor wiring line STG and the common electrodewiring line COM are not formed in the gate layer and that the firsttransparent pixel electrode EL1 (P) is shaped differently.

In FIG. 25D, the opening CH1 is formed by a photolithography process ina portion of the gate insulating film INS11 that is located above thefirst transparent pixel electrode EL1 (P) near the semiconductor layera-Si made of amorphous silicon.

In FIG. 25E, a film is formed from a metal material and is treated by aphotolithography process to form the source electrode S, the drainelectrode D, and the signal line SIG (not shown) simultaneously. Thislayer is called a drain layer. A heavily doped n-type layer (not shown)which is on the top face of the semiconductor layer a-Si and which isnot covered with the drain layer is removed at the same time when thedrain layer is treated. The source electrode S and the first transparentpixel electrode EL1 (P) are electrically connected to each other throughthe opening CH1 formed in a portion of the gate insulating film INS11that is located above the first transparent pixel electrode EL1 (P).

In FIG. 25F, the passivation film INS12 is formed from SiN. While thepassivation film INS12 is left untreated, a film is formed from a metalmaterial on the passivation film INS12 and is treated by aphotolithography process to form the common electrode wiring line COM.

In FIG. 25G, a film is formed from a transparent conductive materialsuch as ITO and is treated by a photolithography process to form thetransparent counter electrode EL2 (C).

In FIG. 25H, the second insulating film INS2 is formed from SiN, andthen three layers, the gate insulating film INS11, the passivation filmINS12, and the second insulating film INS2, are treated by aphotolithography process at once to form openings (CH2 and CH3) in aportion of the passivation film INS12 and a portion of the secondinsulating film INS2 that are located above the source electrode S.

Lastly, a film is formed from a transparent conductive material such asITO and is treated by a photolithography process to form the secondtransparent pixel electrode EL3 (P) as the one shown in FIG. 24A.

The second transparent pixel electrode EL3 (P) is electrically connectedto the source electrode S through the openings (CH2 and CH3) in aportion of the passivation film INS12 and a portion of the secondinsulating film INS2 that are located above the source electrode S.

The TFT substrate is thus manufactured by conducting a photolithographyprocess nine times in total. The number of times a photolithographyprocess is conducted in the eighth embodiment is larger than in theseventh embodiment by one, and is the same as in the first embodiment.The eighth embodiment therefore has the same effects that are obtainedin the first embodiment. The order in which the steps of FIG. 25A andFIG. 25B are executed may be reversed.

The sectional structures of terminal portions and interlayer connectionportions that are formed by the manufacturing steps of the eighthembodiment are shown in FIGS. 26A to 26D. FIG. 26A shows a terminalportion of the scanning line SCN formed in the gate layer. FIG. 26Bshows a terminal portion of the signal line SIG formed in the drainlayer. FIG. 26C shows a connection portion between the common electrodewiring line COM and the gate layer. FIG. 26D shows a connection portionbetween the common electrode wiring line COM and the drain layer.

The opening in a portion of the gate insulating film INS11 that islocated above the gate layer is covered with the drain layer in order toprevent the treatment of the drain layer from disturbing the gate layer.

The common electrode wiring line COM or the transparent counterelectrode EL2 (C) cannot be connected directly to the gate layer and thedrain layer. Therefore, as shown in FIGS. 26C and 26D, the layer of thetransparent electrode EL3 is connected to the common electrode wiringline COM through the opening formed in a portion of the secondinsulating film INS2 that is located above the transparent counterelectrode EL2 (C), and this layer of the transparent electrode EL3 isused to connect the common electrode wiring line COM to the exposedportion of the drain layer within the openings in the passivation filmINS12 and the second insulating film INS2. The structures of FIGS. 26Band 26D are the same as those of FIGS. 23B and 23D described in theseventh embodiment.

Ninth Embodiment

In the seventh and eighth embodiments, as in the first to fourthembodiments, limitations are put on the material and thickness of thegate insulating film and the passivation film in consideration of thecharacteristics and reliability of the thin film transistor TFT, and aninsulating film used for a storage capacitor is also bound by thelimitations. In the ninth embodiment, as in the fifth and sixthembodiments, the first and second storage capacitors are moved to alayer above the passivation film and are each formed from a dedicatedinsulating film, thereby increasing the degree of freedom in selecting amaterial, a thickness, and the like for the first and second insulatingfilms through which storage capacitors are formed.

FIGS. 27A and 27B are schematic diagrams showing a pixel structure in aliquid crystal display device according to the ninth embodiment of thepresent invention. Shown in FIG. 27A is the sectional structure of apixel, and shown in FIG. 27B is the plan view structure of the pixel onthe TFT substrate side. The sectional structure of FIG. 27A correspondsto a view taken along the line A-A′ illustrated in FIG. 27B.

On a first substrate SUB1, signal lines SIG are formed to intersect withscanning lines SCN with a gate insulating film INS11 interposedtherebetween. Each pixel defined by the intersecting scanning lines SCNand signal lines SIG is provided with a thin film transistor TFT, afirst transparent pixel electrode EL1 (P), which functions as the firsttransparent electrode and is shaped like a flat board, and a secondtransparent pixel electrode EL3 (P), which functions as the thirdtransparent electrode.

The second transparent pixel electrode EL3 (P) has a planar shape withslit-like openings SLT which run parallel to one another. Alternatively,the second transparent pixel electrode EL3 (P) may have a planar shapelike a slip or a comb.

The first transparent pixel electrode EL1 (P) between a passivation filmINS12 and a first insulating film INS1 is electrically connected to asource electrode S of the thin film transistor TFT through an opening(contact hole) CH1 formed in a portion of the passivation film INS12that is located above the source electrode S.

The second transparent pixel electrode EL3 (P) which is above a secondinsulating film INS2 is electrically connected to the first transparentpixel electrode EL1 (P) through openings (CH2 and CH3) formed in aportion of the first insulating film INS1 and a portion of the secondinsulating film INS2 that are located above the first transparent pixelelectrode EL1 (P).

A transparent counter electrode EL2 (C), which functions as the secondtransparent electrode and doubles as a storage capacitor electrode, isformed between the first insulating film INS1 and the second insulatingfilm INS2. The transparent counter electrode EL2 (C) has an opening SPKdistanced from the openings (CH2 and CH3), which are formed in the firstinsulating film INS1 and the second insulating film INS2 to electricallyconnect the second transparent pixel electrode EL3 (P) and the sourceelectrode S to each other, by at least a minimum insulation distance. Afirst storage capacitor Cst1 is formed between the first transparentpixel electrode EL1 (P) and the transparent counter electrode EL2 (C)through the first insulating film INS1. A second storage capacitor Cst2is formed between the transparent counter electrode EL2 (C) and thesecond transparent pixel electrode EL3 (P) through the second insulatingfilm INS2. A laminate made up of the gate insulating film INS11 and thepassivation film INS12 below the first transparent pixel electrode EL1(P) constitutes a third insulating film INS3.

A common electrode wiring line COM which is shaped after the shape ofthe scanning line SCN and the signal line SIG and which doubles as astorage capacitor wiring line STG is formed between the first insulatingfilm INS1 and the transparent counter electrode EL2 (C). The transparentcounter electrode EL2 (C) and the common electrode wiring line COMdirectly overlap each other to be electrically connected to each otherand thereby lower the overall resistance of the counter electrode.

A first alignment film AL1 for aligning a liquid crystal layer LC in agiven direction is formed in the topmost layer of the TFT substrate.

On a second substrate SUB2, a light shielding film (black matrix) BM, acolor filter FIL whose color varies from one pixel to another, aprotective film (overcoat) OC, and a second alignment film AL2 areformed to obtain a counter substrate.

The first alignment film AL1 and the second alignment film AL2 are eachprocessed in advance so that liquid crystal molecules are aligned in agiven direction. The first substrate SUB1 and the second substrate SUB2are arranged such that their alignment film formation faces are opposedto each other across a predetermined interval, and the gap between thetwo is filled with a nematic liquid crystal composition having apositive dielectric anisotropy to form the liquid crystal layer LC.

The liquid crystal display device of this embodiment employs an IPSmethod electrode arrangement in which an electric field having acomponent parallel to the surface of the first substrate SUB1 isgenerated between the transparent counter electrode EL2 (C) and thesecond transparent pixel electrode EL3 (P) through the liquid crystallayer LC to form a pixel capacitor Cpx.

A retardation plate and polarization plate (not shown) are disposedoutside of the first substrate SUB1 and the second substrate SUB2 toobtain an NB display mode liquid crystal display device.

Drive circuits (not shown) are connected to the scanning lines SCN, thesignal lines SIG, and the common electrode wiring lines COM. Anequivalent circuit that represents a single pixel in the ninthembodiment is the same as the one described in the second embodimentwith reference to FIG. 7.

FIGS. 28A to 28H show steps of manufacturing the TFT substrate in theliquid crystal display device according to the ninth embodiment. FIGS.28A to 28C are the same as FIGS. 22A to 22C described in the seventhembodiment.

In FIG. 28D, the passivation film INS12 is formed from SiN, and then thegate insulating film INS11 and the passivation film INS12 are treated bya photolithography process at once. An opening (contact hole) CH1 isformed in a portion of the passivation film INS12 that is located abovethe source electrode S.

In FIG. 28E, a film is formed from a transparent conductive materialsuch as ITO and is treated by a photolithography process to form thefirst transparent pixel electrode EL1 (P). The first transparent pixelelectrode EL1 (P) is electrically connected to the source electrode Sthrough the opening CH1 in the passivation film INS12.

In FIG. 28F, the first insulating film INS1 is formed from SiN. Whilethe first insulating film INS1 is left untreated, a film is formed froma metal material on the first insulating film INS1 and is treated by aphotolithography process to form the common electrode wiring line COM.

In FIG. 28G, a film is formed from a transparent conductive materialsuch as ITO and is treated by a photolithography process to form thetransparent counter electrode EL2 (C).

In FIG. 28H, the second insulating film INS2 is formed from SiN, andthen the first insulating film INS1 and the second insulating film INS2are treated by a photolithography process at once to form openings (CH2and CH3) in a portion of the first insulating film INS1 and a portion ofthe second insulating film INS2 that are located above the firsttransparent pixel electrode EL1 (P).

Lastly, a film is formed from a transparent conductive material such asITO and is treated by a photolithography process to form the secondtransparent pixel electrode EL3 (P) as the one shown in FIG. 27A.

The second transparent pixel electrode EL3 (P) is electrically connectedto the first transparent pixel electrode EL1 (P) through the openings(CH2 and CH3) in a portion of the first insulating film INS1 and aportion of the second insulating film INS2 that are located above thefirst transparent pixel electrode EL1 (P).

The TFT substrate is thus manufactured by conducting a photolithographyprocess nine times in total.

The steps of FIGS. 28A to 28E can be adopted from a manufacturingprocess of a fully transmissive liquid crystal display device that hasalready proven its effectiveness in mass production. Then, foursubsequent steps are added to the steps of FIGS. 28A to 28E.

In the ninth embodiment, one more insulating films are formed than inthe eighth embodiment, but the number of times a photolithographyprocess is conducted in the ninth embodiment is the same as in theeighth embodiment. The ninth embodiment can thus increase the degree offreedom in selecting a material, a thickness, and the like for the firstand second insulating films through which storage capacitors are formedwithout adding many steps to the manufacturing process of the eighthembodiment.

The sectional structures of terminal portions and interlayer connectionportions that are formed by the manufacturing steps of the ninthembodiment are shown in FIGS. 29A to 29D. FIG. 29A shows a terminalportion of the scanning line SCN formed in the gate layer. FIG. 29Bshows a terminal portion of the signal line SIG formed in the drainlayer. FIG. 29C shows a connection portion between the common electrodewiring line COM and the gate layer. FIG. 29D shows a connection portionbetween the common electrode wiring line COM and the drain layer.

The transparent electrode EL1 is formed as shown in the drawings inorder to prevent the simultaneous treatment of the first insulating filmINS1 and the second insulating film INS2 from disturbing the gateinsulating film INS11 and the passivation film INS12.

The common electrode wiring line COM or the transparent counterelectrode EL2 (C) cannot be connected directly to the gate layer or thedrain layer. Therefore, as shown in FIGS. 29C and 29D, the layer of thetransparent electrode EL3 is connected to the common electrode wiringline COM through the opening formed in a portion of the secondinsulating film INS2 that is located above the transparent counterelectrode EL2 (C), and this layer of the transparent electrode EL3 isused to connect the common electrode wiring line COM to the gate layeror the drain layer through the exposed portion of the layer of thetransparent electrode EL1 within the openings in the first insulatingfilm INS1 and the second insulating film INS2.

Tenth Embodiment

FIGS. 30A and 30B are schematic diagrams showing a pixel structure in aliquid crystal display device according to the tenth embodiment of thepresent invention. FIG. 30A shows the sectional structure of a pixel,and FIG. 30B shows the plan view structure of the pixel on the TFTsubstrate side. The sectional structure shown in FIG. 30A corresponds toa view taken along the line A-A′ illustrated in FIG. 30B.

The tenth embodiment is a modification example of the eighth embodiment,and differs from the eighth embodiment described with reference to FIGS.24A and 24B in the following points.

Instead of being connected directly to the source electrode S of thethin film transistor TFT through the opening in the gate insulating filmINS11, the first transparent pixel electrode EL1 (P) is connected to thesecond transparent pixel electrode EL3 (P) through openings formed inthe gate insulating film INS11, the passivation film INS12, and thesecond insulating film INS2, and hence the first transparent pixelelectrode EL1 (P) is electrically connected to the source electrode Sthrough the second transparent pixel electrode EL3 (P).

To accommodate this modification, openings (CH1 to CH3) for electricallyconnecting the second transparent pixel electrode EL3 (P) and the firsttransparent pixel electrode EL1 (P) to each other are formed in additionto openings (CH4 and CH5) that are formed in the passivation film INS12and the second insulating film INS2 in order to electrically connect thesecond transparent pixel electrode EL3 (P) and the source electrode S toeach other.

The opening SPK of the transparent counter electrode EL2 (C) in thetenth embodiment is shaped to be at least a minimum insulation distanceapart from the openings (CH4 and CH5) that are formed in the passivationfilm INS12 and the second insulating film INS2 in order to electricallyconnect the second transparent pixel electrode EL3 (P) and the sourceelectrode S to each other, and from the openings (CH1 to CH3) forelectrically connecting the second transparent pixel electrode EL3 (P)and the first transparent pixel electrode EL1 (P) to each other. Anequivalent circuit that represents a single pixel in the tenthembodiment is the same as the one in the second embodiment which isshown in FIG. 7.

In FIG. 30B where additional openings (CH1 to CH3) are formed in thegate insulating film INS11, the passivation film INS12, and the secondinsulating film INS2 in order to connect the second transparent pixelelectrode EL3 (P) and the first transparent pixel electrode EL1 (P) toeach other, the opening SPK of the transparent counter electrode EL2 (C)are larger than in FIG. 24B. The transparent counter electrode EL2 (C)accordingly has a smaller region where the slit-like openings SLT areprovided to apply an electric field to the liquid crystal layer LC, andthe aperture ratio is lowered compared to FIG. 24B. However, thestructure of FIG. 30B has an advantage over the structure of FIG. 24B inthat the number of TFT substrate manufacturing steps in the tenthembodiment is one step less than in the eighth embodiment, as describedbelow.

FIGS. 31A to 31G show steps of manufacturing the TFT substrate in theliquid crystal display device according to the tenth embodiment. FIGS.31A to 31C are the same as FIGS. 25A to 25C described in the eighthembodiment except for the shape of the first transparent pixel electrodeEL1 (P).

In FIG. 31D, a film is formed from a metal material and is treated by aphotolithography process to form the source electrode S, the drainelectrode D, and the signal line SIG (not shown) simultaneously. Thislayer is called a drain layer. A heavily doped n-type layer (not shown)which is on the top face of the semiconductor layer a-Si and which isnot covered with the drain layer is removed at the same time when thedrain layer is treated.

In FIG. 31E, the passivation film INS12 is formed from SiN. While thepassivation film INS12 is left untreated, a film is formed from a metalmaterial on the passivation film INS12 and is treated by aphotolithography process to form the common electrode wiring line COM.

In FIG. 31F, a film is formed from a transparent conductive materialsuch as ITO and is treated by a photolithography process to form thetransparent counter electrode EL2 (C).

In FIG. 31G, the second insulating film INS2 is formed from SiN, andthen three layers, the gate insulating film INS11, the passivation filmINS12, and the second insulating film INS2, are treated by aphotolithography process at once to form openings (CH4 and CH5) in aportion of the passivation film INS12 and a portion of the secondinsulating film INS2 that are located above the source electrode S. Atthe same time, openings (CH1 to CH3) are formed in a portion of the gateinsulating film INS11, a portion of the passivation film INS12, and aportion of the second insulating film INS2 that are located above thefirst transparent pixel electrode EL1 (P).

Lastly, a film is formed from a transparent conductive material such asITO and is treated by a photolithography process to form the secondtransparent pixel electrode EL3 (P) as the one shown in FIG. 30A.

The second transparent pixel electrode EL3 (P) is electrically connectedto the source electrode S through the openings (CH4 and CH5) in aportion of the passivation film INS12 and a portion of the secondinsulating film INS2 that are located above the source electrode S. Thesecond transparent pixel electrode EL3 (P) is electrically connected tothe first transparent pixel electrode EL1 (P) through the openings (CH1to CH3) in a portion of the gate insulating film INS11, a portion of thepassivation film INS12, and a portion of the second insulating film INS2that are located above the first transparent pixel electrode EL1 (P).

The TFT substrate is thus manufactured by conducting a photolithographyprocess eight times in total. In other words, the number of times aphotolithography process is conducted in the tenth embodiment is smallerthan in the eighth embodiment by one, and is the same as in the secondembodiment.

An effect obtained in the tenth embodiment is that the aperture ratiocan be improved more easily than in the second embodiment because thecommon electrode wiring line COM is shaped so as to overlap the scanningline SCN flatly with the gate insulating film INS11 and the passivationfilm INS12 interposed between the two. The order in which the steps ofFIG. 31 and FIG. 31B are executed may be reversed as in the eighthembodiment.

Terminal portions and interlayer connection portions that are formed bythe manufacturing steps of the tenth embodiment are the same as those inthe seventh embodiment which are shown in FIGS. 23A to 23D.

Eleventh Embodiment

The eleventh embodiment is a modification example in which an organicinsulating film FPS is formed from photosensitive acrylic resin or thelike on the passivation film in the IPS liquid crystal display devicesaccording to the first to tenth embodiments.

FIGS. 32A to 32J show modification examples of the sectional structuresof the pixels on the TFT substrate side in the first to tenthembodiments, respectively.

In FIGS. 32A, 32B, 32G, 32H, and 32J, the capacitance of the firststorage capacitor Cst1 formed between the transparent electrode EL2 andthe transparent electrode EL1 is prevented from dropping by not formingthe organic insulating film FPS in a region where the transparentelectrode EL2 and the transparent electrode EL1 overlap each other withthe first insulating film INS1 interposed between the two to form thefirst storage capacitor Cst1.

On the other hand, the organic insulating film FPS is formed in regionswhere the transparent electrode EL2 overlaps the scanning line SCN, thecommon electrode wiring line COM, and the signal line SIG, to therebylower the capacitance of parasitic capacitors.

In FIGS. 32C and 32D, the capacitance of the second storage capacitorCst2 formed between the transparent electrode EL3 and the transparentelectrode EL2 is prevented from dropping by not forming the organicinsulating film FPS in a region where the transparent electrode EL3 andthe transparent electrode EL2 overlap each other with the secondinsulating film INS2 interposed between the two to form the secondstorage capacitor Cst2.

On the other hand, the organic insulating film FPS is formed in regionswhere the transparent electrode EL3 overlaps the scanning line SCN andthe signal line SIG, to thereby lower the capacitance of parasiticcapacitors.

In FIGS. 32E, 32F, and 32I, forming the organic insulating film FPS in aregion where the first storage capacitor Cst1 is formed and in a regionwhere the second storage capacitor Cst2 is formed does not influence thecapacitance of the first storage capacitor Cst1 and the second storagecapacitor Cst2. Accordingly, the organic insulating film FPS is formedavoiding openings (CH1 and CH2) in a portion of the passivation filmINS12 and a portion of the first insulating film INS1 that are locatedabove the source electrode S of the thin film transistor TFT. Thisreduces the capacitance of the parasitic capacitors between thetransparent electrode EL1 and the scanning line SCN and between thetransparent electrode EL1 and the signal line SIG, and levels the pixelsurface as well.

In any of the above-mentioned cases, the additional step of forming theorganic insulating film FPS increases the number of the TFT substratemanufacturing steps. However, since the capacitance of a parasiticcapacitor is lowered by providing the TFT substrate with the organicinsulating film FPS, degradation in image quality can be preventedwithout increasing the capacitance of storage capacitors much.

In FIGS. 32E, 32F, and 32I, a reflective electrode may be formed along aminute concave-convex structure, which is formed in at least part of theorganic insulating film FPS in the display area within a single pixel.This makes it possible to apply the structure of this invention to atransflective or reflective liquid crystal display device that has aninternal diffuse reflection structure.

In FIGS. 32E and 32I, part of the common electrode wiring line COM canbe used as a reflective electrode. In FIGS. 32F and 32I, a reflectiveelectrode may be provided as a component separate from the commonelectrode wiring line COM. It is preferred in this case to form thereflective electrode below or above the transparent electrode EL1 sothat the minute concave-convex structure is reflected well. In any ofthose cases, the reflective display portion may be provided with aliquid crystal layer thickness adjusting layer.

When the structures of FIGS. 32A, 32B, 32C, 32D, 32G, 32H, and 32J areapplied to a transflective liquid crystal display device, the reflectivedisplay portion may be constituted of the organic insulating film FPSwith a minute concave-convex structure which is formed in at least partof the display area within a single pixel and a reflective electrodewhich is formed above the organic insulating film FPS. Desirably,however, the organic insulating film FPS is not formed in thetransmissive display portion, and hence a sufficiently large storagecapacitor is secured. This way, the organic insulating film FPS placedin the reflective display portion also functions as a liquid crystallayer thickness adjusting layer.

In FIGS. 32A, 32B, 32C, 32D, 32G, 32H, and 32J, a light shielding film(black matrix) BM may be formed from an insulating material in place ofthe organic insulating film FPS. The light shielding film BM on the sideof the second substrate SUB2 in this case is not always necessary.

In FIGS. 32E, 32F, and 32I, a color filter FIL whose color varies fromone pixel to another may be provided in place of the organic insulatingfilm FPS. The color filter FIL on the side of the second substrate SUB2in this case is not always necessary.

Twelfth Embodiment

The twelfth embodiment discusses an example of the structure of avertical-field driven liquid crystal display device. In vertical fielddriving where the liquid crystal layer LC is driven by a major electricfield generated in the thickness direction of the liquid crystal layerLC, the third transparent electrode EL3 which is closest to the liquidcrystal layer LC on the TFT substrate side needs to function as a pixelelectrode P.

FIGS. 33A to 33H are schematic diagrams showing the sectional structuresof a pixel on the TFT substrate side in a liquid crystal display deviceaccording to the twelfth embodiment.

FIGS. 33A, 33C, 33E, and 33G show structures in which the seventh totenth embodiments are applied to a vertical-field driven liquid crystaldisplay device, respectively, and correspond to the TFT substrate sidesectional structures shown in FIGS. 21A, 24A, 27A, and 30A,respectively.

FIGS. 33A, 33C, 33E, and 33G merely differ from FIGS. 21A, 24A, 27A, and30A in that the second transparent pixel electrode EL3 (P) does not haveslit-like openings which run parallel to one another, that thetransparent electrode EL2 is a storage capacitor electrode that does notdouble as a counter electrode, and that the metal wiring line below thetransparent storage capacitor electrode EL2 (ST) is accordingly thestorage capacitor wiring line STG instead of the common electrode wiringline COM. A TFT substrate manufacturing process of this embodiment cantherefore adopt the steps shown in FIGS. 22A to 22G, the steps shown inFIGS. 25A to 25H, the steps shown in FIGS. 28A to 28H, and the stepsshown in FIGS. 31A to 31G.

Terminal portions and interlayer connection portions in this embodimentcan have the same structures as the ones shown in FIGS. 23A to 23D, theones shown in FIGS. 26A to 26D, the ones shown in FIGS. 29A to 29D, andthe ones shown in FIGS. 23A to 23D.

FIGS. 33B, 33D, 33F, and 33H show modification examples in which anorganic insulating film FPS is formed from photosensitive acrylic resinor the like on the passivation film in the vertical-field mode liquidcrystal display devices of FIGS. 33A, 33C, 33E, and 33G, respectively.

In FIGS. 33B, 33D, and 33H, the capacitance of the first storagecapacitor Cst1 formed between the first transparent pixel electrode EL1(P) and the transparent storage capacitor electrode EL2 (ST) isprevented from dropping by not forming the organic insulating film FPSin a region where the transparent storage capacitor electrode EL2 (ST)and the first transparent pixel electrode EL1 (P) overlap each otherwith the first insulating film INS1 interposed between the two to formthe first storage capacitor Cst1.

On the other hand, the organic insulating film FPS is formed in regionswhere the transparent storage capacitor electrode EL2 (ST) overlaps thescanning line SCN and the signal line SIG, to thereby lower thecapacitance of parasitic capacitors.

In FIG. 33F, forming the organic insulating film FPS in a region wherethe first storage capacitor Cst1 is formed and in a region where thesecond storage capacitor Cst2 is formed does not influence thecapacitance of the first storage capacitor Cst1 and the second storagecapacitor Cst2. Accordingly, the organic insulating film FPS is formedavoiding an opening (CH1) in a portion of the passivation film INS12that is located above the source electrode S of the thin film transistorTFT. This reduces the capacitance of the parasitic capacitors betweenthe first transparent pixel electrode EL1 (P) and the scanning line SCNand between the first transparent pixel electrode EL1 (P) and the signalline SIG, and levels the pixel surface as well.

Providing the TFT substrate with the organic insulating film FPS lowersthe capacitance of a parasitic capacitor, and degradation in imagequality can therefore be prevented without increasing the capacitance ofstorage capacitors much.

Components of the liquid crystal display device on the side of thesecond substrate SUB2 are omitted from FIGS. 33A to 33H, but a fourthtransparent electrode EL4 which serves as a counter electrode is formedfrom a transparent conductive material such as ITO on a face of thesecond substrate SUB2 that is close to the liquid crystal layer. Thefourth transparent electrode EL4 also functions as the common electrodewiring line COM.

FIG. 34A shows an equivalent circuit that represents a single pixel inthe liquid crystal display device according to the twelfth embodiment.The first transparent pixel electrode EL1 (P), the second transparentpixel electrode EL3 (P), or the source electrode S is provided with aparasitic capacitor Cgs, which is formed between the gate (G) and source(S) of the thin film transistor TFT, and parasitic capacitors Cds1 andCds2, which are formed by the electrode EL1, EL3, or S and the signallines SIG, in addition to the first storage capacitor Cst1, the secondstorage capacitor Cst2, and the pixel capacitor Cpx.

As in all the other embodiments, when the pixel dimensions are reducedto obtain fine pixels, an equivalent storage capacitor sufficientlylarge in relation to the parasitic capacitors including Cgs, Cds1, andCds2 can be formed from the parallel capacitance of the first storagecapacitor Cst1 and the second storage capacitor Cst2.

This makes the voltage of the second transparent pixel electrode EL3 (P)less susceptible to feed-through voltage, which is caused by a voltagechange in the scanning line SCN or the signal line SIG, during a holdperiod in which the thin film transistor TFT is off. Phenomena calledsmearing and cross talk can thus be prevented.

It also reduces the leakage of accumulated electric charges from thefirst transparent pixel electrode EL1 (P), the second transparent pixelelectrode EL3 (P), and the source electrode (S) during a hold period,thereby allowing the electric field applied to the liquid crystal layerLC to drop less. Accordingly, degradation in image quality can beavoided.

Furthermore, since the first storage capacitor Cst1 and the secondstorage capacitor Cst2 are constituted of the first transparent pixelelectrode EL1 (P), the first insulating film INS1, the transparentstorage capacitor electrode EL2 (ST), the second insulating film INS2,and the second transparent pixel electrode EL3 (P), which are alltransparent, forming a storage capacitor that is sufficiently large inrelation to the parasitic capacitor does not lower the aperture ratio ofthe transmissive display portion. The formation of a sufficiently largestorage capacitor and the securing of a sufficiently high aperture ratioare thus accomplished simultaneously.

As in the seventh to tenth embodiments, the storage capacitor wiringline STG and the transparent storage capacitor electrode EL2 (ST) in onepixel row may be separated from those in another pixel row to receivevoltage application independently of those in the other pixel row, orthe storage capacitor wiring line STG and the transparent storagecapacitor electrode EL2 (ST) in one pixel column may be separated fromthose in another pixel column to receive voltage applicationindependently of those in the other pixel column, although, from thestandpoint of reducing the resistance of the storage capacitor wiringline, it is preferred to connect the storage capacitor wiring line STGand the transparent storage capacitor electrode EL2 (ST) in one pixel tothose in adjacent pixels so that a voltage is applied commonly to allpixels.

The voltage of the storage capacitor wiring line STG, namely, thevoltage of the transparent storage capacitor electrode EL2 (ST), may bethe same as the voltage of the fourth transparent electrode EL4, whichdoes not mean that the two always need to match.

A second storage capacitor wiring line STG2 may be formed in the gatelayer below the source electrode S, to thereby form a third storagecapacitor Cst3 between the source electrode S and the second storagecapacitor wiring line STG2 through the gate insulating film.

The third storage capacitor Cst3 in this case constitutes an equivalentcircuit as the one shown in FIG. 34B. A voltage is applied to the secondstorage capacitor wiring line STG2 commonly to all pixels, orindividually on a pixel row basis. The voltage of the storage capacitorwiring line STG and the voltage of the second storage capacitor wiringline STG2 may be the same, which does not mean that the two always needto match.

The structure of the twelfth embodiment is also applicable to areflective or transflective liquid crystal display device that employs avertical-field driven liquid crystal display mode.

In this case, a reflective electrode is formed in at least part of oneof the first transparent pixel electrode EL1 (P), the transparentstorage capacitor electrode EL2 (ST), and the second transparent pixelelectrode EL3 (P) to be used as the reflective display portion, whichmay be provided with a liquid crystal layer thickness adjusting layer.

FIG. 33F, in particular, can be applied to a transflective or reflectiveliquid crystal display device that has an internal diffuse reflectionstructure if a reflective electrode is formed along a minuteconcave-convex structure, which is formed in at least part of theorganic insulating film FPS in the display area within a single pixel.

Part of the storage capacitor wiring line STG may be used as areflective electrode. Desirably, however, a reflective electrodeseparate from the storage capacitor wiring line STG is formed below orabove the first transparent pixel electrode EL1 (P), and hence theminute concave-convex structure is reflected well.

In the case where FIGS. 33B, 33D, and 33H are applied to a transflectiveliquid crystal display device, the reflective display portion may beconstituted of the organic insulating film FPS with a minuteconcave-convex structure which is formed in at least part of the displayarea within a single pixel and a reflective electrode which is formedabove the organic insulating film FPS.

Desirably, however, the organic insulating film FPS is not formed in thetransmissive display portion, and hence a sufficiently large storagecapacitor is secured. In this way, the organic insulating film FPSplaced in the reflective display portion also functions as a liquidcrystal layer thickness adjusting layer.

In FIGS. 33B, 33D, and 33H, a light shielding film (black matrix) BM maybe formed from an insulating material in place of the organic insulatingfilm FPS. The light shielding film BM on the side of the secondsubstrate SUB2 in this case is not always necessary.

In FIG. 33F, a color filter FIL whose color varies from one pixel toanother may be provided in place of the organic insulating film FPS. Thecolor filter FIL on the side of the second substrate SUB2 in this caseis not always necessary.

The second transparent pixel electrode EL3 (P) does not have slit-likeopenings SLT in the vertical-field driven liquid crystal display deviceaccording to the twelfth embodiment. Alternatively, the secondtransparent pixel electrode EL3 (P) may have an opening for controllingthe alignment of liquid crystal molecules as in the vertical alignment(VA) display mode. Besides, a dielectric projection for controlling thealignment of liquid crystal molecules may be formed on the secondtransparent pixel electrode EL3 (P).

The vertical-field driven liquid crystal display mode discussed here maybe a known technology such as the VA mode, the TN mode, the ECB mode,the OCB mode, the polymer dispersed type, and the like.

In all of the above-mentioned embodiments, a retardation plate may beadded if necessary for a desired display mode and, conversely, may beremoved if not necessary. For example, when the guest-host display modeis employed, the polarization plate may also be removed if notnecessary. Besides, the retardation plate and the polarization plate maybe placed not only outside but also inside of the first substrate SUB1and the second substrate SUB2.

A columnar spacer may be placed on at least one of the opposing faces ofthe first substrate SUB1 and the second substrate SUB2. With thecolumnar spacer, the liquid crystal layer LC can have a uniformthickness throughout the plane of the liquid crystal display device.

Further, a backlight is provided on the opposite side of the displaysurface of the liquid crystal display device.

The alignment of the liquid crystal layer employed can be horizontalalignment, twisted alignment, vertical alignment, hybrid alignment, andthe like.

As has been described above, in each of the above-mentioned embodiments,an equivalent storage capacitor sufficiently large in relation to theparasitic capacitors can be formed from the parallel capacitance of thefirst storage capacitor Cst1 and the second storage capacitor Cst2. Thismakes the voltage of the pixel electrode less susceptible tofeed-through voltage, which is caused by a voltage change in thescanning line or the signal line, during a hold period in which the thinfilm transistor TFT is off. Phenomena called smearing and cross talk canthus be prevented, and degradation in image quality is prevented.

It also reduces the leakage of accumulated electric charges from thepixel electrode and the source electrode (or the drain electrode) duringa hold period, thereby allowing the electric field applied to the liquidcrystal layer to drop less. This prevents luminance shading andunevenness in a displayed image without raising the voltage output fromdrive circuits and without increasing power consumption.

Further, since the first storage capacitor and the second storagecapacitor are both transparent in the transmissive display area, forminga storage capacitor that is sufficiently large in relation to theparasitic capacitors does not lower the aperture ratio of thetransmissive display portion, and the luminance in transmissive displayis prevented from dropping. The formation of a sufficiently largestorage capacitor and the securing of a sufficiently high aperture ratioare thus accomplished simultaneously.

The invention made by the present inventors has been describedconcretely through the above-mentioned embodiments. However, the presentinvention is not limited to the above-mentioned embodiments and ismodifiable in various ways without departing from the spirit of theinvention.

What is claimed is:
 1. A liquid crystal display device comprising: afirst substrate; a second substrate; and a liquid crystal held betweenthe first substrate and the second substrate, wherein the firstsubstrate has a transparent pixel electrode formed in each pixel; asecond insulating film covering the transparent pixel electrode; acommon wiring line formed on the second insulating film from a metalmaterial; and a transparent counter electrode opposed to the transparentpixel electrode across the second insulating film, the transparentcounter electrode being formed on the second insulating film and thecommon wiring line to electrically connect with the common wiring line.2. A liquid crystal display device according to claim 1, wherein a firstinsulating film, the transparent pixel electrode, the second insulatingfilm, the common wiring line, and the transparent counter electrode arelaminated in this order from the first substrate, the first insulatingfilm has a contact hole formed thereon a transparent electrode patternis formed in a same layer as the transparent pixel electrode, thetransparent pixel electrode, the second insulating film, the commonwiring line, and the transparent counter electrode are laminated aroundthe contact hole.
 3. A liquid crystal display device according to claim1, wherein the transparent pixel electrode is connected with a thin filmtransistor formed in each pixel through a contact hole formed on a layerlower than the transparent pixel electrode, the transparent counterelectrode has multiple slits formed therein and includes a portionlocated in the contact hole, at least one of the multiple slits isformed in the portion of the transparent counter electrode.
 4. A liquidcrystal display device according to claim 2, wherein the transparentpixel electrode is connected with a thin film transistor formed in eachpixel through a contact hole formed on the first insulating film, thetransparent counter electrode has multiple slits formed therein andincludes a portion located in the contact hole, and at least one of themultiple slits is formed in the portion of the transparent counterelectrode.
 5. A liquid crystal display device according to claim 1,wherein the transparent counter electrode extends to cover the commonwiring line.
 6. A liquid crystal display device according to claim 2,wherein the transparent counter electrode extends to cover the commonwiring line.
 7. A liquid crystal display device according to claim 5,wherein the transparent counter electrode has a larger width in adirection along a scanning line than that of the transparent pixelelectrode, and the transparent counter electrode has a larger width in adirection along a signal line than that of the transparent pixelelectrode.
 8. A liquid crystal display device according to claim 6,wherein the transparent counter electrode has a larger width in adirection along a scanning line than that of the transparent pixelelectrode, and the transparent counter electrode has a larger width in adirection along a signal line than that of the transparent pixelelectrode.